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Marine Biological Laboratory Library ffl

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ffi August, 1954 ffl

IB I

Adventures WITH ANIMALS AND PLANTS

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ANIMALS

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AND

PLANTS

BT
ELSBETH KROEBER
WALTER H. WOLFF

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*^ -« - GENERAL BIOLOGY

D. C. HEATH AND COMPANY
BOSTON

The Authors

ELSBETH KROEBER is First Assistant in Biological Science; Adminis-
trative Assistant at the Midwood High School, Brooklyn, New York. She
was formerly Chairman of the Department of Biology^ at James Madison
High School, Brooklyn, New York.

WALTER H. WOLFF is Principal of the William CuUen Bryant High
School, Queens, New York. Among his former positions are the follow-
ing: Instructor, School of Education, The City College, College of the
City of New York, and Chairman of the Department of Biology and
General Science, DeWitt Clinton High School, Bronx, New York.

THE ILLUSTRATIONS

The cover design for this book was executed by Richard Bartlett from a
drawing by W. A. Dwiggins, the frontispiece and title page ^^'ere painted
by Else Bostelmann, the text drawings were made by Paul Wenck and
Joseph Lenhard, and the diagrams by iMagnuson and Vincent. The photo-
graphs reproduced in the text are acknowledged where they occur. The
montage on page z was assembled with the professional assistance of
Marion Howe.

No parr of the material covered by i.his copyright mav be rcpro-
ducctl in an\- form without written permission of the jiubhslier.

Offices: Boston New York Chicago Atlanta
Sax Francisco Dallas LoNiX)N

Printed in the United States of Avieridx (504)

PREFACE

As you begin the study of biology you
begin a most exciting adventure, the
study of animals and plants — the living
things of the earth. You are one of these
living things, so you will learn much
about yourself. The study of living
things is not only exciting; it is impor-
tant to all mankind. Our knowledge of
biology has made it possible for us to
avoid many diseases, to provide more
and better food, and to understand our-
selves better.

The study and teaching of biology is
the lifework of many people. They are
professional biologists. It is possible that
you will make the study of biology your
lifework. If so, you will find much in
this book to help you toward that goal.
In writing Adventures ivith Animals and
FlajJts, however, the authors had in
mind, principally, the much larger num-
ber of people who will not become pro-
fessional biologists. All of us need to
know many of the facts and principles
of biology in order to understand our-
selves and make the best use of many of
the things we see, hear about, and read
about.

Whether or not you make biology
your lifework, you will want to know
how a professional biologist works and
thinks, how he discovers the facts and
principles that are so useful to all of us.
Biologists, and other scientists as well,
use a special method of discovering

and testing facts and principles. It is
called the scientific method. As you
study this book, the scientific method
will be brought to your attention many
times.

Hygiene, which is the science of main-
taining health and the prevention of dis-
ease, is based upon a knowledge of many
parts of biology. Throughout the book
you will find information that will be
useful to you in keeping healthy.

We learn the facts and principles of
biology by three methods. One is by ob-
serving animals and plants, a\ riting down
what we observe, and comparing what
we see with what others have learned.
By a second method we also use observa-
tion, but we observe and interpret the
results of an experiment which was set
up to try to answer some question or
problem. A third method is to read what
others have learned bv the use of the
first two methods. In using- this book
you will make use of all three methods:
you will read, you will observe, and
you will experiment. Perhaps, if you are
a keen observer, or become one, you will
discover something no one else has ever
learned.

In this book you will read about many
of the facts that biologists have learned
by observations and experiments; and
you will learn what conclusions or prin-
ciples have been stated to summarize or
explain the facts. You will frequently

Vlll

find suggestions for helpful class discus-
sions and for experiments that will either
add to the information contained in the
text or make the text discussions more
clear. These suggestions are grouped at
the end of each Problem and are called
Exercises. At the most appropriate places
in each Problem these Exercises are re-
ferred to. You cannot possibly do all of
them; the authors hope you will find
time to do many of them. Each of these
Exercises has been chosen with great care
to help you understand some part of bi-
ology, to help you to learn how a biolo-
gist works (the scientific method), or to
help you to find out something new.

The Questions at the ends of the Prob-
lems are designed for your use in re-
viewing what you learn in studying the
Problem. If you can answer all the Ques-
tions, you can feel pretty sure that you
have done a good job on that section of
the text.

If you are one of those who like biol-
ogy very much, you will want to try
some of the Further Activities in Biology
that are listed at the end of each Prob-
lem. You may also wish to read some of
the many books and articles that are
listed at the end of the book, just before
the Index.

Since this book was designed to fit the
courses of study in schools throughout

Preface

the United States, it may contain some
topics that are not required in your
school. Therefore your teacher may pre-
fer not to assign certain sections of it.
Some sections are marked "Optional."
These may be omitted, if your teacher
so desires, without interfering with your
understanding of the parts that follow.

All the authors' long experience in
teaching, directing other teachers, and
writing for students has been applied to
the writing of this text, which is a suc-
cessor to Adve?inires with Livmg Things.
To insure accuracy, the authors have
asked a number of people to read por-
tions of this book. In addition to the
large number of specialists who critically
read many portions of the authors' earlier
text, they wish now to thank: Mr.
Aiaurice Bleifeld, Chairman, Department
of Biology, Newtown High School,
Queens, N. Y.; Professor A. L. Kroeber,
Emeritus, University of California; Pro-
fessor Laurence H. Snyder, Dean, The
Graduate College, University of Okla-
homa; and Dr. Charles Tanzer, DeWitt
Clinton High School, New York Citv.
The authors thank also Airs. Charlotte O.
Wolff for assistance in preparing the
Index.

Elsbeth Kroeber
Walter H. Wolff

TABLE OF CONTENTS

Introduction: Biologists Study Aiiiuials and Plants

JJjiit

I. THE LIVING THINGS OF THE EARTH ARE MANY
AND VARIED

Problem i. What Kinds of AniTimls Inhabit the Earth? 15

The Vertebrates i6

The Invertebrates 39

Problem 2. What Ki?ids of Plants hi habit the Earth? 72

Flowerless Plants 73

Plants with Flowers and Seeds 80"

Problem 3. Hoiv Are Livijig Things Named and Classified? 95

II. ALL LIVING THINGS ARE BASICALLY ALIKE 104

Problem i. Of What Are All Living Things Composed? 105

Problem 2. How Do Their Activities Keep Cells Alive? 118

Problem 3. How Are the Cells Arranged in Anijnals and Plants? 129

III. GREEN PLANTS MAKE THE FOOD USED

BY ALL LIVING THINGS 136

Problem i. What Part Do Leaves Play i?i Making and Using Foods? 137
Problem 2. What Part Do Roots and Ste?ns Play i?i Maki?ig

and Usi?ig Food? 148

IV. HOW A COMPLEX ANIMAL USES FOOD FOR ENERGY

AND GROWTH 166

Problem i. How Can We Choose Foods Wisely? 167

Problem 2. How Does the Digestive System Make Foods Usable? 188

Problem 3. How Are Materials Moved to and from Our

Body Cells? 206

Problem 4. How Are All Our Cells Provided with a Constant

Supply of Oxygeji? 226

Problem 5. How Does the Body Get Rid of Wastes Formed

by Cell Activity? 237

Problem 6. What Substances Help Regidate Cell Activities? 246

68951

X Tciblc of Contents

Unit

V. WHY Ll\ ING THINGS BEHAVE AS THEY DO 260

Problem 1. What Arc the Simplest Forms of Bcl^avior in Animals? 261
Problem 2. What Makes Coinplex Behavior Possible iji

Many-celled Animals? 269
Problem ^. Hove Does the Behavior of Complex Ani/nals Differ

from That of Simpler Forms? 286

Problem 4. Hov: Do Plants Respojid to Their Enviroiimoit? 301

VI. CONSTANT CARE IS NEEDED FOR MAINTAINING

OUR HEALTH 310

Problem 1. Hove Are Our Bodies Protected against Microorga/nsi/is? qii
Problem 2. ]]'hat Have Scientists Learned about Conqneriiiir

Sovie Covnnon Diseases? 320

Problem 3. {Optional) How Have Recent Discoveries Changed

Some of Our Ideas about Disease? 338

Problem 4. Hove Do We Attevipt to Stop the Spread of Disease? 343

Problem 5. Ho\e May We Achieve Better Health for All? 359

Ml. HOW IJ\ ING THINGS AFFECT ONE ANOTHER 372

Problem i. TF/m? Makes Possible the Continued Existence of Plants

and Anntials? 373

Problem :. What Are Our Relationships to Other Organisms? 381

Problem ^ Hove Do We Try to Solve Our Insect Problevis? 389

P1UIBLEM 4. Why Must We Practice Conservation? 399

\ III. now ANIMALS AND PLANTS MAKE MORE OF THEIR

OWN KIND 410

Problem 1. Hov: Do the Simple Anii/ials and Plants Reproduce? 411

Problem 2. How Do the More Complex Annuals Reproduce? 421

Problem ^ Hove Do the More Complex Plants Reproduce? 438

IX. THE ORGANISM IS THE PRODUCT OF ITS HEREDITY

AND ITS EN \' I RON Ml- NT 454

Problem i. Why Do Off spring Resemble Their Parents? 455
Problem 2. Hov: Can Some of the Differences between Parents

and Offspring Be Explained? 464

Problim 3. How Can New Hereditary Characters Appear? 479
Problem 4. How Does the Environment Affect the Characters of

an Organism? 485

Table of Contejtts

Unit

Problem 5. What Have We Learned about Frodiicing Neiv Types
of Animals and Plants?

Problem 6. To What Exte?n Can Mankind Be biiproved?

X. THE EARTH AND ITS INHABITANTS HAVE CHANGED
THROUGH THE AGES

Problem i. What Can We Learn from Rocks about the History

of the Earth?
Problem 2. What Can We Learn from Fossils about Prehistoric

Living Things?

Problem 3. What PiLZzUng Facts May Be Explained by Onr Theory
of the Origin of Neiv Organisms?

Problem 4. What Theories Have Been Offered to Explain the
Origin of Different Kinds of Animals and Plants?

Problem 5. What Were the Stages of Man's Development
on the Earth?

BIBLIOGRAPHY

GLOSSARY

INDEX

493

508

520

521
533
547

564

580

583
599

Hoxv To Use This Book

1. How this book is organized. Adven-
tures ivith Aniinals and Plants is divided
into Units, each of which presents a
major topic in biology. When you have
rinished studying a Unit you will have
learned the most important facts pre-
sented in that Unit, and should under-
stand the important ideas gro^ving out of
those facts. To aid you in reaching this
understanding, each Unit is divided into
two or more Problems. These Problems
may be said to be the chapters of the
book. Each Problem title poses a ques-
tion, the answer to which is to be ob-
tained by studying the text that follows.

When the answers to all the Problem
questions contained in a single Unit are
understood, you will have all the infor-
mation necessary to an understandincr of
the statement at the head of that Unit.

Each Problem is composed of "para-
graphs" headed by a title in boldface
type. Each of these paragraphs supplies
some information necessary for arriving
at the answer to the Problem question.
A simple, step-by-step study of the para-
graphs, as suggested in the following sec-
tion, will help to put vou on the road to
success in your biology course.

2, How to learn from this book. There

Xll

are many devices in this book designed
to help you to learn biology readily. Of
these, the Unit headings, Problem ques-
tions, and paragraph titles are the most
important, because they tell you what
you are supposed to learn. From the
very beginning of any study period you
should know what you are trying to
learn. After reading a paragraph title,
think over the meaning of the title and
ask yourself what, you already know
about that subject. When vou have
thought through and organized your
previous knowledge, you will be better
equipped to grasp the additional infor-
mation that is supplied by the book. You
will find it helpful to do the Exercises
referred to throughout the text as vou
are studying the section those Exercises
are intended to supplement. Perhaps the
class as a whole can plan with the teacher
how to do some of the Exercises. This is
more interesting than following direc-
tions laid down by others.

If, at first reading of the text, you do
not understand a sentence, finish the par-
agraph to find out if your questions are
answered. Then go back and re-read the
sentence as it stands in relation to the
rest of the paragraph. If you still have
questions, make a note of them and have
them explained in class. If it is a word
that vou do not understand, look it up.
If that is not possible, make a note of the

How to Use This Book

word so that you can learn its meaning
in class. The field of biology makes use
of many special words that you will
need to learn. These words are printed in
italics and defined when they first ap-
pear. If you do not recall the meaning of
a word when it is used later in the book,
look it up in the Index to find where it
was used first. A good way to learn the
special vocabulary of biology is to pre-
pare a glossary for yourself in your note-
book. A glossary is simply a special dic-
tionary. You can list the new terms you
learn and write their definitions in your
own words. As a basis on which to build
your o\\ n more complete list of words
you will find a glossary prepared by the
authors beginning on page 583.

There are many illustrations in this
book. Every one has been chosen to add
to your understanding and information.
It will be useful for you to look at them
carefully and to study the legends.

Both the printed text and the illustra-
tions will undoubtedly raise questions in
your mind. These are the most precious
results of study because they lead to
interesting class discussions and, later, to
a more complete understanding of the
subject. Such questions will also empha-
size to you that in biology, as in other
sciences, there is much that remains to be
learned.

Adventures WITH ANIMALS AND PLANTS

Fk;. I All aviumls and plants are subjects for biologists to study. Students of biology
learn what kinds of living things there are, how they are constructed, how they re-
maiii alive, why they behave as they do, how they reproduce, why they reseynble their
parents, why there are so many kinds, how they are dependent upon each other, how
vtan ajjects them, and how they affect man. (photos by cruicksiiank-nationai, audu-

BON society, national ZOOLOGICAL SOCIETY, TYRELL-NATIONAL AUDUBON SOCIETY, PHILIP
GENDREAU, UAI.PII ANDERSON, AND MUSEUM OF NATURAL HISTORY)

Biologists Study Animals and Plants

What is biology? Biology is the study
of Hving things. This means that biology
is the study of all animals, including
man, of all plants, and of those simple
living things which we do not know
whether to call animal or plant. Since
biology is the study of all living things,
all of us have been biologists (students
of biology) in a small way all of our
lives. When you learned the name of the
robin you were, for the moment, a bi-
ologist. To be more exact you were a
zoologist (zoh-ol'-o-jist), a student of
animals. Would it make it seem more
important if you knew that this branch
of zoology was called ornithology, the
study of birds? You were learning biol-
ogy w^hen you noticed that a dog would
dash after a ball (the science of animal
behavior) and when you noted green
leaves come out in the spring (botany,
the science of plants). You were an
unwilling biologist, too, when you had
measles or scarlet fever and discovered
how other organisms can affect man.

Evidently biology is the study of
living things in any way in which a
biologist wants to study them. You may
think that this makes biology a large
and varied science — and so it does.
There are many sub-sciences that make
up the larger science of biology. You
have just read the names of a few of
them; there are many others which you
will read about in this book.

What to study about living things.
Most people will say that one of the
first things to learn about a living thing
is its name. This is true. Most of the
living things you see frequently have
common names and you will want to
learn some of them. You can learn to
know an oak tree from a maple tree
and a woodchuck from a skunk. In
some cities you will see maples, elms,
and poplars along the streets; in others
palms and pepper trees. You will enjoy
knowing these names as well as the
names of common breeds of dogs and
cats and of many other animals and
plants.

But more important than the names
of living things is a knowledge of their
structure; that is, the parts of which a
living thing is made and how these parts
fit together to make a whole orgaiiism
(or'gan-ism), a single living thing.
Since you are more interested in your-
selves than in any other organism, it is
especially useful to you to know the
structure of your body. When you
have completed a year's work in biology,
you will know something about how
you and all other human beings are
constructed: what your heart is like
and your stomach and your brain and
the other parts of your body. Of course
in one year's time you will not be able
to learn very much about living things.
The men and women who spend their

entire lives studying just one part of
biology do not then feel that they have
mastered it completely.

The knowledge of how organisms are
constructed becomes especially valuable
when you go on to learn how organisms
carry on life activities. If you know
how vou digest and absorb food, how
you breathe, how your blood circulates,
how your actions are controlled, how
it happens that human beings are like
their parents, and how human beings
have developed through the ages, you
will have important information about
yourself. To understand this w^ell you
will need to learn something about the
structures of other organisms, such as
lower animals and even plants, and how
they carry on their life activities.

Man and other living things. There
are even better reasons for learning how
other organisms carry on their life ac-
tivities. Consider plants; it is important
to you and to me that plants be raised
for our use. If the wheat crop is a great
deal smaller than usual, we may have
less bread; if the corn crop fails, cattle
and hogs are scarcer and the price of
meat goes up. In fact, if there were no
plants on this earth we would not be
here at all.

Then consider the many animals such
as rabbits, moles, and particularly in-
sects, that injure crops and interfere
with the production of food and mak-
ing a living. There are also many organ-
isms that attack man directly, causing
disease. It is well to know something
about all these organisms and to know
how we can protect ourselves and our
crops against them. Men are constantly
affected by other living things.

Biologists Study Anmials and Planus

The work of biologists. Since the field
of biology is so large, the work of bi-
ologists is varied. Some biologists live
out of doors, exploring and learning
about plants and animals at first hand
by observation and recording. Some
biologists work in the laboratory, ex-
perimenting with living things or with
chemicals in test tubes; some study
plants or animals at close range through
the microscope to learn the secrets of
living matter. Before you plunge into
the study of living things let us see how
some of these biologists do their w^ork.

Biologists explore the world. Do vou
know what kinds of plants and animals
live on this earth? Do you know w^hat
plants and animals live on the island
of Borneo or along the Amazon River?
Could you describe a scene in the Gobi
Desert of Asia or picture to yovu'self
the plants that make summer beautiful
within the Arctic Circle?

It seems that similar questions have
always interested man. There have al-
ways been men bold and adventurous
enough to undertake long voyages to
distant parts of the earth merely to see
and collect the plants and animals liv-
ing there.

About two hundred years ago Carolus
Linnaeus (lin-nee'us), a young student
at a Swedish university, was sent by his
country to Lapland to make collections
of living things. He started alone, carry-
ing in his leather bag a simple micro-
scope, a telescope, paper for drying
plants, and writing materials for taking
notes. For many months he endured
great hardships. During this time he
reached the Arctic Ocean on foot. Then
he returned to his university with a few

Biologists Study Aimnals mid Plants

specimens of rocks and animals and
plants, and complete notes on every-
thing he had seen. He had learned a
great deal about the customs of the
native Lapps, had become acquainted
with the wild animals of the country,
and had made a thorough study of the
plants, for botany was the subject of
greatest interest to him. It is said that
he traveled more than four thousand
miles.

Linnaeus' accounts of his journey in-
spired other biologists to explore foreign
lands. Often these trips last for several
years during which the biologist is far
from any civilized country, completely
dependent upon his ability to make
friends with native tribes. He has to
win their confidence slowly, learn their
language, and persuade them to take long
trips on foot, on horseback, or by boat
through parts of the country the natives
may fear. Here the explorer devotes
himself to his search for new types of
animals and plants. Many of these are
collected and stored to be taken back
to museums and universities. Complete
notes are kept of all observations so that
no mistake will be made when the scien-
tific reports are later prepared. Some of
these exploring scientists are also excel-
lent artists and prepare their own
sketches of the strange scenes they see.

Exploring is not at an end. Exploring
nowadays is frequently very complex.
Large expeditions are organized. They
include experts in many branches of
science and are equipped with scientific
instruments of many kinds. Photog-
raphers and secretary-historians are
among the specialists included. Despite
their size, such expeditions still meet

B"» ../ k.... ■-..:' --tf^'- i'>^ . .'t-'i'iT^^.

Fig. 2 What water-living plants and ani?nals
might this collector find? (ward's natural

SCIENCE establishment)

with exciting adventures. Even as you
read this, investigators are at work in
the field in many parts of the world,
searching high in the mountains, and
deep in the sea, , in the frozen wastes of
the arctic and antarctic, and in the hot,
wet jungles.

Exploring the depths of the ocean. You
may join exploring biologists in imagi-
nation, if you wish. Would you care to
stroll through a garden in the warm
seas twenty feet below the surface? Get
into your bathing suit, strap your div-
ing helmet to your shoulders, and climb
down the ladder that hangs over the
side of the boat. When you reach the
last rung, drop off. You will sink gently
to the bottom. Take care not to scratch
yourself on the corals that are part of
the lovely undersea gardens. If you have
remembered your zinc pad and lead

Biologists Study Ani?nals and Plants

Fig. 3 The Central Asiatic
expedition of the American
Museii/u of Natural History
jueets with an accident in
the Mongolian Desert. What
abilities iiiiist the explorer
have besides a knowledge of

biology? (AMERICAN MU-
SEUM OF NATURAL HISTORY)

'VM^*.*?V,**"^i«

Fig. 4 Exploring in a jtmgle.
Dr. Williaju Beebe and two
fellow scientists take motion
pictures of living things oji
the floor of a jungle in
Venezuela, (jocelyn crane

—NEW YORK ZOOLOGICAL SO-
CIETY)

pencil, you will be able to take notes
as soon as your eyes grow accustomed
to the dim light.

The sunlight filters through this clear
tropical water and flashes from the bril-
liant reds and yellows of the many kinds
of fish. The beauty of the ocean floor
with its brightly colored animals will
delight y<JU as it has the biologists who
have gone down many times to study
this active world of living things. Some
have described its beauties, others have
painted its scenes, and still others have

photographed the graceful forms so that
everyone may now enjoy the gardens
undersea. When the ^\'ater is clear and
not too deep, living things in the sea
can be seen through panes of glass in
the bottom of a boat. Diving in a helmet
has many advantages, however. And
now that helmets have been perfected
almost anyone can explore the shallow
seas. But for exploration down to a
depth of half a mile a bathysphere is
used. This is a ball of steel with thick
glass windows and a powerful electric

Biologists Study Aimnals and Plants

Fig. 5 Photographed ojf the Florida coast. What
inforjuation can biologists obtain by under-
water trips? How else caji they get such infor-
mation? (miller dunn co.)

light casting a beam out into the sur-
rounding blackness.

Long before these methods of study-
ing the life of the sea had been de-
veloped, other devices were in use. Nets
made of steel had been dragged on the
bottom of the sea, sometimes as much as
three miles down, and then hauled to the
surface so that the catch might be
studied. Nets had been invented that
could be dragged through the water at
certain depths and closed before they
were pulled in. In this way biologists

would know, for example, that certain
fish live at depths of half a mile, coming
no closer to the surface nor going much
farther down. Dredges with steel jaws
had been dropped to the bottom and
closed so that samples of the sand and
ooze (mud) could be collected and
examined. This disclosed the fact that
the thousands of square miles of ocean
bottom is the graveyard of tiny animals
whose skeletons sank after death. A
single one of these tiny animals is too

small to be seen by the naked eye yet

the countless billions that have died
have formed thick deposits of this ooze.
Thus slowly the labors of many men
are making it possible to describe life
in the darkness of the ocean depths.

Exploring nearer home. Not all biolo-
gists interested in getting acquainted
with plants and animals have wandered
to the far corners of the earth to dis-
cover and describe them. Many have
remained at home, knowing that with
patient observation much could be
learned about animals and plants nearby.

One of the most famous of the stay-
at-home observers was Jean Henri Fabre
(fah'br). For most of the years of his
long and useful life Fabre watched the
insects in his garden and in the sunny
fields. He would crouch, motionless, for
long hours at a stretch, intently watch-
ing the behavior of some insect. It was
by such patient observation that he saw
insects hunt food and store it, fight
enemies, and mate. He saw how eggs
were laid and how they hatched. Then
he wrote exact descriptions of what he
had seen. He left many simple and inter-
esting accounts of his observations;
most of them have been translated from

Biologists Study Animals and Planzs

Fig. 6 An outdoor museum, part of the Nature Trail at Tuxedo, New York. Could
you build a simple nature trail? What besides names might be given on the various
tags that you see? (American museum of natural history)

the French so that you can read them.

Other stay-at-home observers may
study birds, or snakes, or other animals.
Such study can satisfy a love of the out
of doors and add to the store of bio-
logical knowledge.

Backyard exploration for you. Equipped
with a pad and a pencil, you too can
start on a tour of exploration. You may
fill notebooks with your observations of
the wild things in a park, in a field, or
in a city lot. You can collect specimens
and lay out a museum of your own.

Or you may choose to mark off a
small plot on the bank of the creek
flowing by your house, the edge of a
nearby wood, or a city yard. If you
study this with care you w ill be amazed
at the many organisms you will find.
One biologist collected several hundred
different kinds of insects from his own
small backyard in three years.

Your backyard may be only a roof
or a window sill. A sheltered board
regularly supplied with bread crumbs
will bring passing birds, A piece of sod
brought in from out of doors and
watered carefully will grow into a
miniature jungle. There will be much
for you to observe and many experi-
ments for you to try. With a camera
you can add to the pleasure of backyard
exploration and provide a treasured
album.

A study of biology can lead to many
outdoor hobbies: the collecting of in-
sects, fossils, shells, or plants; the raising
of pets such as guinea pigs, rabbits, and
white mice; the studying of insects in
their homes; the planting and care of a
oarden.

The biologist's laboratory. While some
biologists explore, many more work in
the laboratory — the workshop of the

Biologists Study Anivials and Plmts

Fig. 7 A corner of the Boy
Scout Museum at Bear
Mountain, New York. What
suggestiotis for hobbies does
this picture give you?

(AMERICAN MUSEUM OF NAT-
URAL history)

scientist. The well-equipped workshop
has sinks with faucets of different sizes;
stone tables with vacuum and air pres-
sure outlets and connections for gas
and electricity; rows of shelves for bot-
tles of dyes, acids, testing agents, glass-
ware of many kinds, and some reference
books; cupboards with microscopes,
dissectingr instruments and other instru-
ments of various sorts. There may be an
incubator, a pressure cooker, a refrig-
erator. The laboratory is the place in
which biologists perform their "labors,"
in which they investigate, observe, ex-
periment, draw conclusions, and record
their studies of living things. That is
why boys and girls who set up little
places at home for the study of living
things may speak of them as biologists'
workshops or laboratories.

A peep into a laboratory. The great
Russian biologist, Ivan Pavlov ( 1 849-

1936), in the early years of the present
century wished to learn something of
animal behavior. Let us visit him in his
laboratory. He used dogs as experimental
animals because they M^ere easy to work
with. Pavlov wanted to find out how
the saliva can be made to flow in a dog.
But before he could begin his experiment
he had to perform a difficult operation.
He opened a small hole in the dog's
face and inserted a tube to which a jar
was attached. When Pavlov showed
food to the dog, the saliva flowed into
the jar and the amount could be
measured. It took weeks to train the
do^- to stand still in a harness while he
was fed. After these preparations Pavlov
was ready for his experiment. He rang a
bell each time he put food before the
doer. This was continued for some time.
Then, one day, Pavlov rang the bell
without putting the food before the

Biologists Study Animals and Plants

Fig. 8 (left) The viodern
research ftiicroscope is far
different from the siviple in-
strument of Leeuwenhoek^s
day. (spencer lens co.)

Fig. 9 (right) One of Leeii-
wenhoek's many micro-
scopes. A lens was fastened
into the metal plate. The
rest of the microscope is the
object holder, which, by the
use of screws, was used to
place the object in proper
position. Compare this with
the moder7i research micro-
scope, (bausch and lomb)

dog. The saliva flowed from the dog's
mouth just the same and in the same
amounts. This experiment was per-
formed many times, and with many dif-
ferent dogs. Always the sound of the
bell made the flow of saliva start.

Then Pavlov varied his experiment; in
one variation, as he showed the food he
touched the dog on its hindquarters
instead of ringing a bell; in another
variation he showed the food and at the
same time showed the dog a paper on
which a large circle had been drawn.
In each experiment, after enough repe-
titions there was a flow of saliva even
when the food was withheld. Pavlov
showed in this way that not only the
normal cause, but also an unusual cause,
could lead to the flow of saliva in the
dog. The experiments taught scientists
something about the way in which
animals learn. You will read more about
this later in the book.

But notice how carefully the stage
was set for the experiment. Weeks

spent in training the dog; years of study
to make possible the delicate operation;
skillful construction of the cages and
harness; patient watching for results;
accurate measurement and recording of
the facts day after day; the repetition
of the experiment with many dogs —
all this was necessary to make successful
w^hat may have seemed to you at first
to have been a relatively simple job.

Biologists study the "invisible." The
man who first saw "invisible" or micro-
scopic creatures was a Dutchman, Anton
van Leeuwenhoek (163 2- 1723), whose
hobby was making lenses. When he had
ground and polished a small bead of
glass until he was sure it would magnif\'
well, he used it to examine all kinds of
tiny objects to find out what they
really looked like.

It was a great day for him and for
biologN' when he examined a drop ot
the rain water that had been standing in
a barrel. Picture his amazement and de-
light when he found that the drop was

Biologists Study Animals and Plants

Fig. io The 7nan is using an
electron 7/ncroscope. With
its use it is possible to obtain
photographs 200,000 times as
large as the objects. Yon can
see that the electron micro-
scope bears no resemblance
to the compound micro-
scope, (r.c.a.)

a little world of wriggling, squirming
creatures never before seen by man.
When he reported his discovery, men
in other countries used their lenses to
examine similar drops of water. They,
too, saw these living things that had
been invisible until then. They studied
them, filled notebooks with descriptions
of their activities, and drew careful dia-
grams to illustrate their structures.

The biologist improves his tools. As
microscopes were improved, smaller
and smaller living things were found
and examined. Today, good microscopes
enable us to study objects so tiny that
50,000 of them laid end to end would
measure only one inch. But increase in
magnifying power has not been the
only advance. More important than that

has been the increase in clearness of
vision.

Modern microscopes are impressive
instruments of shiny enamel and polished
chromium but improvement in appear-
ance is much less important than the
improvements in the lenses. They are
marvels of fine grinding, far, far better
than any in the early microscopes.
Modern instruments are unlike the
early ones in another way; they magnify
twice, by two sets of lenses. They are
therefore called compound microscopes.
The two magnifications are multiplied.
If the lens near the object magnifies fifty
times and the lens near the eye ten
times, the total magnification is 500. The
microscope that biologists or physicians
use can generally magnify 1 800 times.

Biologists Study Animals and Plants

Fig. 1 1 Dr. Alexander Flem-
ing in his laboratory, exam-
ining some mold cultures in
test tubes. You ivill read
7/iore abo2it his great con-
tribution to the world. He
discovered the drug, peni-
cillin, (wide world)

Ultraviolet and electron microscopes.
In using the ordinary microscope we
use light that the eye can see. A little
over forty years ago it was discovered
that one could obtain higher magnifica-
tion by using ultraviolet light. Ultra-
violet light cannot be seen by the human
eye but can be photographed. By this
means magnifications of 4000 or even
higher are possible. Objects that had
been invisible under the best microscope
could now be seen. More recently an
electron microscope based on new prin-
ciples has been invented. Recent im-
provements have given us a microscope
that magnifies 20,000 times. Then by
enlarging the negatives a magnification
of about 200,000 times can be obtained!
In just a few years biologists have suc-
ceeded in photographing objects that
no one had ever hoped to see. You may
expect the newspapers and magazines to

carry exciting accounts of new discov-
eries in the future as the electron micro-
scope is applied to living things and new
facts are learned about their tiniest
parts.

The study of living things goes on. All
the world over there are biologists, both
men and women, as well as boys and
girls, who continue to study living
things. Their activities are as varied as
the activities of the living things that
they study. There are so many problems
to study — there is so much we do not
yet know — that biological study is end-
less and always fascinating.

A glance at the newspaper will dis-
close the fact that discoveries are being
made daily. As this is written it is knowxi
that there are four or more kinds of
penicillin made by mold plants. They
have been used successfully to combat
certain types of disease germs. But we

Biologists Study Anivials a?id Plants

do not yet know how these types of
penicilhn differ or what the chemical
make-up of penicilhn is. By the time
you read this it is likely that much more
will be known about this spectacular
drug.

The problem of cancer is of tremen-
dous interest to men and women. How
can we detect it as soon as it starts so
that we can save a human life? What
causes it? Do we know exactly how
such organs as the liver and the spleen
function in man? How do vitamins act
to prevent certain diseases? Is "intelli-
gence" — whatever it is — inherited? If
so, how? If not, what produces it? What
can we do to improve it in boys and
girls? What makes us act as we do?

And basic to all these questions: What
kind of material is the living stuff in all
plants and animals? Will we ever be
able to make such living stuff in the
laboratory?

There are thousands of such questions
that can be asked, and, fortunately, there
are thousands of men and women in
every country trying to answer them.

The most fascinating part of the study
of biology is that at any moment a com-
plete or a partial answer to a problem
may be provided. When you read this
book you may know the answer to a
question that the authors did not know
when they wrote it. The pursuit of
biological knowledge goes on always
with continuing success.

In UNIT I you "will consider these problems:

Problem i . \\^hat Kinds of Animals Inhabit the Earth?
Problem 2. What Kinds of Plants Inhabit the Earth?
Problem 3. How Are Living Things Named and Classified?

UNIT 1 THE LIVING THINGS OF THE EARTH ARE
MANY AND VARIED

Fic;. 12 jLcbras and gnus at a water hole in Sotith Africa. Some biologists prefer to
study the anivials a7id plants of foreign lands. Others are most interested in those
that live near by. (south African railways)

PROBLEM

1 What Kinds of Animals Inhabit the Earth?

The animal kingdom. We often speak
of two large groups of animals: the
v^ertebrates, animals with a backbone;
and the invertebrates, animals without a
backbone. A backbone consists of sep-
arate little bones {vertebrae — ver'te-
bree). The vertebrate group is very
large and is subdivided into five classes:
the mammals, the birds, the reptiles
(snakes and their relatives), the am-
phibians (frogs and their relatives), and
the fish. All these animals, diff^erent as
they may seem at first glance, have im-
portant resemblances. Besides the back-
bone, they all have a brain in a boxlike
skull {craniinn). Attached to the brain
is a spinal cord. It lies along the animal's
back, protected by the backbone. All
animals having these characteristics are
called vertebrates.

The vertebrates, together with some
other less familiar animals, are called
chordates (core'dates). We shall not refer
again to the other chordates. The name
phyhmi (fy'lum) is given to such a big
grouping as the chordates.

The invertebrates are arranged in
many groups or phyla (fy'la). There are
many more kinds of invertebrates than
vertebrates. And the number of individ-
uals is much larger, too. Commonly
known invertebrates are the insects, the
spiders, the lobsters, the clams, the snails,
the starfish, the worms, the jellyfishes,
the corals, the sponges, and the mi-
croscopic animals known as protozoa

(proe-toe-zoe'ah). All these belong to
the animal kingdom. So the ants which
are insects have as much right to be
called animals as dogs or horses or birds.
All belong to the animal kingdom.

Subdividing the animal kingdom. You
read that the animal kingdom is divided
into large groups called phyla. A phylum
may be divided into subphyla; generally
it is divided into classes. Now this book
and many other textbooks are divided
into units and the units are subdivided
into problems and the problems into para-
graphs. On more or less the same prin-
ciple a phylum is divided into classes and
the class is divided into orders. In a later
problem you will see that the subdivid-
ing does not stop there; it goes right on
until you have the followmg:

Phylum
Class
Order
Family
Genus
Species

The word species (spee'shees) means
kind of animal (or plant) such as the
dog species or cat species, the lion species,
the horse species, and so on. Sometimes
the species is subdivided even further
into varieties or breeds.

In reading about animals in this prob-
lem you will concern yourselves mostly
with phyla and classes and some of the
species of animals they include.

The Liv'mg Things of the Earth unit i

chimpanzee

Robin

Lizard

Frog

Codfish

Fig. 13 Exmnpks of each of the five chief classes of vertebrates.

The Vertebrates

CLASS -MAMMALS

How we can recognize mammals. A4am-
mals have a backbone; they are verte-
brates. But thev differ from the other
vertebrates in that they have hair or fur.
Some mammals have very httle hair;
there is little hair on an elephant's body
and even less on a whale's. But every
vertebrate with any hair at all is a mam-
mal. The other striking distinguishing
characteristic of all mammals is the
lummnary or milk glands by which the
young are fed. Mammals breathe by
means of lungs and they are warm-
blooded (that is, their body temperature
is fairly constant; it does not change
much with changes in the temperature
of the surroundings) but these are not
characteristics that make them different
from all other vertebrates because birds,
too, have lungs and are warm-blooded.
Mammals also have two pairs of legs
but so do all frogs and some reptiles as
well. There are about 4000 species of
mammals. Because of their complex
structure they are spoken of as the

"highest" animals. This would be a good
time for \'ou to begin Exercise i.

Man and the apes. Mammals are sub-
divided into groups (called orders). The
group most important to us is the one
containing ourselves. All mammals are
somewhat like man in structure but the
great apes, such as the chimpanzees, the
gorillas, and the orangutans, resemble
man in structure much more closely
than do any other animals. For this
reason man and the apes are placed in
the same group. The monkeys also belong
to this group.

Mammals with grinding teeth. This
is a large group. It really includes sev-
eral orders. You probably know giraffes,
deer, buffalos, cows, gazelles and goats;
horses and zebras; elephants; and rhi-
noceroses. Most of these animals have
single or double hoofs. The hoof is an
enlarged and thickened toenail. How-
ever, elephants, rhinoceroses, and some
others lack a hoof and hav^e several toes.

All of them have grindinir teeth used
in chewing grass and leaves. Many of
them, such as cows, sheep, deer, and

PROBLEM I. The K}?7ds of A??i?77als of the Earth

Fig. 14 (above) The Civiada /*
lyfix or bobcat, (u. s. bu-
reau OF BIOLOGICAL SURVEY)

Fig. 15 (upper right) Go
rilla. (CHICAGO park dis
trict)

Fig. 16 (right) Camel (NE^v

YORK ZOOLOGICAL SOCIETY)

Why are all of these animals called maimnals? To which groups of inavivials does
each belong? Why is the gorilla placed in the same order as man?

Others have a stomach with a large
pouch which serves as a reservoir for
the food swallowed while the animal
grazes. Later as the animal rests this
food comes up again into the mouth
and is chewed as "cud."

Mammals with long eyeteeth. These
are the carnivores (car'ni-vores). The
long eyeteeth are used for tearing flesh.
But some carnivores eat other foods too.
Bears relish berries and small insects such
as ants. Some, like the hyena, eat car-

The

rion (dead animals). But most carni-
vores hunt and kill. Bears, wolves, foxes,
skunks, and many others have blunt,
strong claws. In cats, tigers, and lions the
sharp claws are pulled back w hen not in
use.

Gnawing mammals. We all know the
gnawing mammals, or rodents. There
are about 2000 species spread over prac-
tically the whole globe, in the hot
desert and in the arctic snow and ice.
Some burrow in the ground, some live
in trees, and others live in the water.
You know rabbits, rats, mice, squirrels,
and woodchucks. You may have seen
beavers, or perhaps the dams they build.
If you live in our West you have heard
the whistling marmot; you have seen the
prairie dogs on our great plains. Most
rodents are small and timid. The two
pairs of front teeth (incisors) can in-
flict an ugly wound but unless cornered
the animal will not bite. The front teeth,
used for gnawing and chiseling, are
worn down by constant use. But they
keep growing as long as the animal
lives.

Mammals that live in the sea. A whale
is so dependent on the water and so
fishlike in shape and general appearance
that at first glance you might not classify
it as a mammal. But it has the two dis-
tinguishing characteristics of a mammal:
it has mammary (milk) glands and its
skin, although mostly naked, has a few
bristles of hair. Like other mammals it
is warm-blooded and brings forth its
young alive. Whales have large amounts
of fat called "blubber." This protects
them against the cold. Alan converts
the fat into oil, obtaining as much as 1 50
barrels of oil from a good-sized whale.

Living Things of the Earth unit i

There have been many fanciful stories
about whales. A \\ hale cannot swallow
a man whole nor does it even attack
man except when fighting back. And
whales do not spout water. When a
whale comes to the surface and breathes
out, the water vapor in its hot breath
condenses (just as yours does on a cold
day) and the little drops of water that
are formed look like a stream of water
shooting up into the air.

There are other mammals that live
in the sea: walruses, seals, and sea lions.
Examination of their structure and par-
ticularly their teeth shows that they are
really carnivores. The seals and sea lions
spend part of the time on land resting
or waddling about awkwardly by using
their flippers as legs.

Mammals that fly. The bats are mam-
mals that fly. They can flv^ better than
many birds. Being mammals, they do
not have feathers; they have hair. Bats
resemble a tailless mouse with bie ears
and large folds of skin under the arms
which are used as wings. All day long
they hang head down, hooked to the
rafters of some buildine^ or in a cave or
hollow tree. Some species sleep in col-
onies of several thousands, coming out
at night to search for food. Most bats
live on insects, some eat fruits, and a
few, the vampire bats, suck the blood
of other mammals. It is not true that
bats fly into people's hair nor do our bats
hurt \'ou in any way.

Simple mammals. The 7f7arsi/pifils
(mar-soo'pee-els) are simpler than the
mammals you have just read about.
Among the marsupials the young are
born in a very undeveloped and helpless
state, and the female carries the young

PROBLEM I . The K'mds of Aimnals of the Earth

Fig. 17 Like all other car-
nivores, the sea lion is
equipped with sharp pointed
teeth, (international news
photos)

Fig. 18 The opossum is the
only ponched rna7}mial foutid
ontside of Australia. }J'hat
7ise does it 7>iake of its tail?
(gehr)

Fig. 19 This picture of a
brown bat shows how the
7He?nbranes attached to body
and legs are stretched out
by the long finger bones.

(AMERICAN MUSEUM OF NAT-
URAL history)

The Living Things of the Earth unit i

Fig. 20 The spiny anteater of Australia and a Fig. 21 The duckbill of Australia. This iinvnnial
model of the egg it has laid. (American museum also lays eggs. (American museum of natural
OF natural history) history)

in a pouch for a long time after birth.
See Figure 384, page 433. The kanga-
roos of Australia and the opossums of
our country belong to this group. In
one common species, the Virginia opos-
sum, the animal when discovered pre-
tends it is dead; it "plays 'possum."
There are several other kinds of mar-
supials in Australia besides kangaroos.
The simplest mammals lay eggs. Duck-
bills lay eggs and have bills like a duck
but since they have mammary glands
and hair they are considered to be mam-
mals. Spiny anteaters and armadillos are
other simple mammals. Now do Exer-
cises 2, 3, and 4. If you would like to
continue your study of mammals, you
will find it useful to refer to some of
the interesting books on mammals listed
in the bibliography at the end of the
book.

CLASS - BIRDS

The characteristics of birds. Birds have
feathers. There are no exceptions. That

is the characteristic by which you recoij-
nize them. The feathers are usually
lacking on the legs, which are covered
with scales. There are two other char-
acteristics almost as striking as the first:
birds have beaks or bills without teeth
and the forelimbs have the structure of
wings.

Birds, like mammals, are \\arm-
blooded; their temperature, in general,
is higher than that of mammals. Some
of them, indeed, have a temperature of
112°. Like mammals they have four-
chambered hearts and they breathe by
means of lungs. There is much that \()u
can discover for yoursrlf if you will fol-
low the directions ir Exercises 5 and 6
carefullv\

Subdivision of the class. This class is
subdivided into many different orders
but the differences between the orders
are technical and difficult to learn. In
this section, we shall use a simple group-
ing based mostly on the kind of feet and
bill: birds of prey, scratching birds,

PROBLEM I . The Kinds of Anmmls

birds that wade or swim, perching birds,
and birds that cannot fly.

Birds of prey. These are the eagles,
hawks, vultures, and owls. Their wings
spread wide and firm; their talons
(claws) are cruel, curved daggers which
can be driven deep into the body of a
small mammal or other bird; their
strong beaks used for tearing flesh are
hooked and sharp. Some hawks, eagles,
and vultures are easily recognized in
flight because of their remarkable ability
to soar, that is, to remain aloft with
almost no movement of the wings. They
do this by taking advantage of the air
currents. In spite of common belief,
birds of prey, with few exceptions, are
useful to man. Their natural food is
rabbits, field mice, other small mammals,
and even certain species of insects which
are destructive to crops.

The vultures and some of their rela-
tives are scavengers; they feed on the
dead and decaying flesh of animals.

of the Earth 21

Scratching birds. These live on the
ground and scratch for seeds and small
insects; such birds are the common
fowl, the grouse or partridge, and the
turkey. Some of these birds are strong
and swift flyers, too, but for the most
part they rely on their legs instead of
their wings. Domestic fowl such as
chickens, ducks, and turkeys have prac-
tically lost the power of flight.

Birds that wade or swim. These are,
mostly, large birds. They squawk and
call hoarsely but never sing. Their food
comes from the water and they spend
much of their time in the water or on
it. The storks, the herons, the cranes,
and the flamingos (fla-ming'gos) wade.
Their tall legs keep their bodies well
out of the water and their long pointed
beaks and flexible necks make it pos-
sible for them to snatch the frogs or
fish that make up their diet.

Among the swimming birds are the
ducks, geese, and swans. Their legs are

Forehead

Upper mandible
Lower mandible
Throat

Wing coverts
Breast

Crown

Claw

Abdomen

Scales

Back

Scapulars
Rump

Upper tail coverts
Lower tail coverts

Heel-joint

Tail
feathers

Fig. 22 This drawing of a mockingbird is labeled to show the nairres of the various
parts. It is helpful to know these na?nes when you are learning to identify birds. Bird
descriptiofis in books use these terms because all students of birds know thetn. Coidd
you describe the colors of a robin or of a canary, using some of these words?

Fic;. 23 A young owl. The owl 1mm s at yilght.
What do you notice about tl?e size of its pupils?
How does this help the owl? (American mu-
seum OF NATURAL HISTORY — OVERTON)

Kic. 24 The American eagle. In which way is it
fitted for obtaining food? (nature magazine —
fisher)

ll?c Living Things of the Earth unit i

strong and attached far back enabling
them to exert a powerful push against
the water. The position of the legs
makes it easy for them to tip their
heads down for a dive. Their feet are
large and webbed.

Water birds all produce much oil
which protects their feathers from get-
ting wet. This fact has given rise to the
common expression, "as water rolls off
a duck's back."

Birds which cannot fly. A few species
live wholly on land and never fly. The
ostrich, the largest living bird, and its
less familiar relatives have ^\'ings which
are too small to be of any use. But all
are good runners, running as fast as
sixty miles an hour. When attacked and
cornered, an ostrich defends itself by
means of a kick which is dangerous to
man.

Perching birds. These, for the most
part, are the birds that sing. You may
kno\\' best the house (English) sparrows
and the starlings of our crowded cities;
the robins and the bluebirds of our
suburbs; or the swallows and the crows
of the countryside. These, and about
four hundred fift\- other species, are
perching birds. They are the birds to
which man omcs much thanks for keep-
ini^- down insect pests and for eating the
seeds of weeds that would spoil crops
and gardens. The songbirds often steal
our fruit, but their bill of fare consists
largely of insects or seeds of weeds
that are harmful to man.

Migration of birds. Many birds and
some other animals migrate. They move
from one place to another and back
airain in tlie course of a year. The
migrating season is generally the spring

PROBLEM I. The Kinds of Anhnals

and the fall. Many of our songbirds
spend the summer in the more northerh'
states and the winter in the south. Some
winter over in the northern states and
fly to the arctic in the spring. iMigrat-
ing birds may perform amazing feats
of flying. The arctic tern, a water bird,
builds its nest in the far north; several
months later it flies to the antarctic.
Although the route has not yet been
completely traced, it is known that these
birds fly about ii,ooo miles each way.
The golden plovers travel a shorter dis-
tance, from Canada to South America,
2000 miles or more, but they fly over the
ocean in one stretch. They complete
the journey in two days and nights
without stopping to rest or feed.

There are many interesting questions
about migration still unsolved. "How
can birds travel so far without food and
rest?" "How can thev find their way?"
"How can some return not only to the
same state and town but to the very
nest in which thev were reared?" And
difficult as any: "Why do birds migrate,
anyway?"

Bird flight. Upward and forward mo-
tion of birds is supplied by a powerful
downward and backward beat of the
wings against the air. The large wing
feathers overlap while the wings beat
backward, but the feathers separate as
the wing comes forward and up. Because
the feathers separate during the forward
motion, little resistance is offered to the
air and not much speed is lost. When
birds soar, they move their wings very
little; instead, they depend on air cur-
rents, just as a glider does.

What helps the bird in its flight? Its
wings are enormously long as compared

of the Earth

Fig. 25 Compare the position of the eyes of this
sandhill crane with the positio?i of the o'wl''s
eyes. Note also the legs and bill, (new york

ZOOLOGICAL society)

Flycatcher \' C^"

Fig. 26 The bill often tells you something about
the bird's food. For what kinds of food is each
bill fitted?

The Livivg Things of the Earth unit i

Fig. 27 Spriiii^ iiiigratioii routes of some comvion birds. Some of these birds follow:)
the same routes south in the fall. Which of these birds travel the loiigest distance?
Some of the 60 species which follow route 2 are the bobolink, chuck-wiW s-widow,
the gray-cheeked thrush, the bank swallow, the black-poll warbler, and the night-
hawk. The picture above the map is of Canada geese taken during migration. You
will find it interesting to find out the migration routes of the Canada goose, (ewing
galloway)

PROBLEM 1. The Kinds of Anv/Jials of the Earth

Fig. 28 Carolina Wren

Fig. 29 Sierra Jiinco

The birds of Figures 28, 29, 30, and 32 are called
perching birds. What do these birds eat? How
are they helpful to man? What can we do to
protect thefn? The birds that built the nests of
Figure 5/ are also helpfid. Can you find out
why? (Fig. 28, HUGH davis; Fig. 2p, nature mag-
azine; Figs. 50, 5/, and 32, American museum
OF natural history)

J-
Fig. 31 Nests of the cliff swallow

Fig. 30 Chickadee

Fig. 32 Hummingbird

The Living Things of the Earth unit i

Fig. 3:5 The garter snake. This snake is one of the conunoiicst found in the United
States. It is frequently seen on farms, even near the bnildings, and frequently, also, in
lawns and gardens of thickly settled connimnities. The garter snake may bite when
it is handled rmighly, but its bite is harmless, except as a possible source of infection.
It does not lay its eggs as many other snakes do. The eggs hatch within the mother s
body and the young are born alive. All snakes move by wriggling and by many small
inoveinents of their ribs which are attached to the sharp scales on their underside.

(U. S. BUIUEAU OF BIOLOGICAL SURVEY)

to the size of the body; there are very
powerful breast muscles which move
these win^s. The breast bone to w hich
the muscles are attached and many other
bones are hollow, making the body ex-
ceptionally light in weight.

In the bibliography at the end of the
book there are listed several books about
birds. Perhaps you will wish to read
one of them and learn more about birds.

CLASS - REPTILES

What is a reptile? Like mammals and
birds, reptiles have lungs. Some la\- eofrs
as do the birds; some bring forth their
young alive. But they differ from mam-
mals and birds in that they are covered
with scales. Scales, you remember, are
characteristic of fish also. How, then,
can one distinguish between reptiles and
fish? This is easy, for fish in ocneral
get air from the water by means of gills.

and their scales arc slinn'. Reptiles have
lungs and dv\ scaly skins.

Reptiles are the first vertebrate ani-
mals you have met in this book that are
cold-blooded. The body of the cold-
blooded animal is sometimes \\arni and
sometimes cold, depending on the sur-
roundings. Reptiles are most common in
the tropics; as you go north\\'ard you
may expect to find fewer and fewer rep-
tiles. In a climate such as that of the
northeastern states where A\inters are
cold, reptiles are active and visible during
only a short season. As fall comes on
they become sluggish and soon go into
a state of hibernation (winter sleep) un-
derground. Some reptiles run on four
legs, some on two, while some wriggle
without an\' legs at all. Many live on
land; others dwell in fresh water or in
the salt\- ocean. Zoologists divide them
into three main orders which \'ou can
easil\ recognize: the snakes and lizards,

PROBLEM I. The Kinds of Animals of the Earth

Fig. ^4 How Tiiciiiy ratllcs
has this rattlesnake'!' It is not
true that one can tell a rattle-
snake's age by the inanber of
rattles, (u. s. bureau of bio-
logical survey)

Fig. 35 The head of a rattle-
snake ready to strike. Where
is the poison gland located
■ivith relation to the fangs?

Poison gland

Poison duct

Fang (foofhj

alligators and crocodiles, and tuxtles.

Our poisonous snakes. The feeling of
horror that snakes arouse in some people
is unreasonable. As a child you may
have seen your elders shrink at the sight
of a snake and you may have learned to
imitate them. Children left to them-
selves have no more fear of snakes than
of any other animals that seem strange.
Most snakes are harmless; poisonous
snakes are the exception. In this country
there are only four kinds of poisonous
snakes: the rattlesnake, the copperhead,
the water moccasin, and the coral snake.
On our continent man is rarely bitten,
even where poisonous snakes are nu-
merous, for with the exception of the
water moccasin our poisonous snakes
are timid; they do not attack unless they
are disturbed. Still more rarely does any
one die of the bite. An understanding of
the methods of treating a bite and the

Gland-squeezing muscle

'y- Jaw-opening
muscle

courage to remain calm almost always
prevent serious results from the poison.

The poison is injected through a pair
of large, hollow, very sharp fangs
(teeth). These are in the upper jaw,
folded back out of the way until the
snake strikes. The swiftly-moving little
tongue contains no poison; the snake
uses it to learn of its surroundings.

Rattlesnakes are widely scattered over
the United States. When disturbed, they
sound their rattles, which are located at
the tip of the tail, so that it is easy to
avoid them. It is only when they are
taken by surprise that they strike with-
out warning. The amount of poison in-
jected depends on the size of the snake.
Large rattlers are therefore more dan-
gerous than small ones. The copperhead
is found in various regions in the north-
ern half of the country. The water
moccasin and the coral snake are not

The Living Things of the Earth unit i

Fig. 36 (above) Aj7 adult copperhead
may be two or two and one half feet
long. As in rattlers and water vioc-
casins, the head is triangiilar. (u. s. bu-
reau OF BIOLOGICAL SURVEY)

Fig. 37 (right) This x-ray photograph
of a snake shows the long backbone
and the 7?iany ribs which help in
locomotion, (general electric x-ray

CORP.)

uncommon in the south. The water moc-
casin, which lives in swamps, is some-
times called "cottonmouth" because the
inside of its mouth is white. The coral
snake is smaller than the water moccasin
and has short fangs but when it bites,
it hangs on, and sometimes its bite is
serious. It often burrows in damp
ground. Do Exercises 7 and 8.

Peculiarities of snakes. Snakes have
an enormously long backbone, consist-
ing of many vertebrae each of which,
except at the tail end, has a pair of ribs.
Muscles connect the ribs with the scales
on the lower part of the snake. By mov-
ing the ribs, the scales are hooked onto
the uneven surface of the ground, one
after the other. Thus the snake really
wriggles on its scales, but this happens

so fast and evenly that it looks like a
smooth gliding motion. No snakes have
legs, although the pythons (pie'thons)
of Asia have tiny stumps of hind legs
which are not used.

Because of its peculiar formation, a
snake's mouth can be opened so wide
that it will admit an animal broader
than the head of the snake. The animal
must be swallowed whole since the
teeth are not used for biting off or chew-
ing food. At irregular intervals as snakes
gro\\' they develop a nt\x skin under-
neatii the old one. The old skin is then
shed as in the photograph. Figure 39.

Snakes of other countries. While snakes
in our part of the world arc not a real
danger, in India, Central and South
America, and other tropical regions

PRDKLEM I. The Kwds oj Annuals oj the Earth

snakes are a serious menace. It is esti-
mated that in India alone they kill about
20,000 people ever^^ year. One of the
most deadly snakes of India is the cobra.
It- is vicious, and injects a particularly
strong venom (poison). There are also
huge pythons in India which reach a
length of more than thirty feet. They
coil themselves around their victims and
crush them to death. Some of the boa
(boh'a) constrictors and anacondas of
the tropical Americas may also reach a
large size. Many reptiles, unlike other
animals, keep on growing throughout
their lives and they live long.

Lizards — the closest relatives of snakes.
People often call the little four-legged,
soft-bodied salamander, so common in
the woods, a lizard; but since it lacks

Fig. 39 (above) A hog-nosed snake losing its
old skin. As a snake grows its skin becomes too
small. A new skin jornis under the old one.

(AMERICAN MUSEUM OF NATURAL HISTORY)

Fig. 38 (left) This swift is a typical lizard.
Notice the claws on its toes. What characteris-
tics of a lizard does it have? Why is it classed
as a reptile? (American m:useum of natural
history)

a scaly covering you know it cannot be
a reptile, and must not be called a lizard.
Lizards have, as a rule, slender bodies
with long tails and four rather short
legs which can move with great speed.
Lizards live in warm climates.

Lizards of the United States are, with
one exception, harmless. The one lizard
which bites and has poison fangs is the
red and black striped Gila (hee'la)
monster. It lives in the deserts of Ari-
zona and New Mexico.

Alligators and crocodiles. Alligators
and crocodiles are large reptiles which
inhabit only the warmer portion of the
globe. Even there they are sluggish,
resting motionless in shallow streams
with their eyes and nostrils above the
surface of the water. However, the sight

The Living Things of the Earth unit i

\'\G. 40 (above) These tadpoles arc the yonn
of the <j;ree/i frof^. How do they differ fro/// on
adult frog? (HUGH spencer)

of some unwary animal along the banks
will quicklv^ rouse them to activity.

Turtles. Turtles have a complete back-
bone, ribs, and all the other bones you
should expect a vertebrate or a "back-
boned" animal to have. The siicll de-
velops from the skin of the uppei* and
lower surfaces and becomes attached
to the backbone and the ribs. Head and
legs are, of course, covered \\'ith the
ordinary scales characteristic of reptiles.
Turtles may eat plants, insects, frogs,
fish, or any other small animals. Their
horny, toothless jaws are sharp and
strong and are used for tearing and

Fig. 41 (left) The s/iappi//ir turtle is fo/i//d in
ponds or rivers. It has a d/ill hroivvish shell iviti?
//otches at the back. Why are turtles classed as
reptiles? (.-vmerican museum of natural his-
tory)

biting, much as teeth are used by othtr
animals. In a few species the shells re-
main soft. To become better acquainted
with reptiles read one of the books
listed in the bibliography.

CLASS - AMPHIBIANS

How we can recognize amphibians

Amphibians, like reptiles, are cold-
blooded vertebrates. Their skin is naked
and in almost all species is soft and
moist. They are called amphibians be-
cause most of them spend the first part
of their life in the water and the other

PROBLEM I. The Kinds of Annuals of the Earth

Fig. 42 A green frog can jinnp fifty times its P'lc. 43 The American toad cannot jump as far
length. What structures make this possible}' as the frog. Can you tell why}' ( Schneider and

(AMERICAN MUSEUM OF NATURAL HISTORY) SCHWARTZ)

part on land. While in the water stage
thev obtain air by means of gills; in the
land stage they use lungs for breathing.
There are a few species which do not
develop lungs at any stage and never
leave the water; when full grown they
resemble a legged tadpole.

Amphibians with tails. Biologists divide
the class Amphibians into two orders —
those with tails and those without. The
tailed forms, the salamanders and newts,
might be mistaken for lizards until one
discovers the moist, naked skin. They
are timid, harmless creatures; their feet
have no claws and their jaws are weak,
unfitted for biting. They catch insects
with the tongue. Some of the tailed am-
phibians are brightly colored; others,
like the hellbender, are dull and un-
attractive. One that many of you may
have found in the woods, under logs
or leaves, is the beautiful red newt.

Amphibians without tails. You are
much more familiar with this group
which includes the frosts and toads.

Thev feed on insects which they catch
with their long, slimy tongue. They
lay their eggs in fresh water; these hatch
into tadpoles which change into adults
as legs and lungs form. Frogs when fully
developed, continue to spend at least part
of their time resting just under the sur-
face of the water with eyes and nostrils
raised above the surface. The hind feet
are webbed and are equally useful for
swimming and jumping. Toads, on the
other hand, leave the pond and return
only in the spring to lay their eggs. Their
skin becomes so dry that it looks shriveled
and warty. The statement that you can
get warts from handling toads was long
ago proved to be untrue. Toads are not
only harmless to us but are a great help
to the gardener because they eat insects.
Do Exercise 9.

CLASS - FISHES

What is a fish? As you turned from
the most complex vertebrates, the mam-

The Living Things of the Earth unit i

Fig. 44 Sharks belong to a group lower than fishes. They have neither true scales nor
bones. Gill covers are lacking. This shark has two shark suckers attached to its lower
side, (new york zoological society)

mals, to the simpler ones, you met first
the birds, then the reptiles, then the
amphibians. There are other cold-
blooded vertebrates even less complex;
these are the fishes. Their distinguishing
characteristics are slimy scales, fins, and

gills. Of course they have a backbone
just as other vertebrates do. They are
water dwellers, obtaining the oxygen
they need from the air dissolved in the
water. Out of water, fish die quickly
because their gills cannot take oxygen
from the atmosphere. Most fish have
paired fins, usually two pairs, and other
fins which occur singly. Make your own
observations of fish by doing Exercises
lo, 1 1, and 12.

"Fish" that are not fish. The animals
of this group are closely related to fish

Dorsal fin

Left nostril

Gill cover Left pectoral fin

Left pelvic fin

but have skeletons made of a softer sub-
stance called cartilage (car'til-aj). You
may know cartilage by the name of
gristle (griss'l). One of the commonest
is the dogfish that destroys large num-
bers of food fishes along the coast.
Sharks are its larger cousins, with repu-
tations often much worse than they de-
serve. Most species of sharks do not
attack man but eat only fish and other
animals of the sea.

Fish are numerous and varied. There
is three times as much sea as land. You
can see that there is plenty of room for
fish. Great numbers live in both \yarm
and cold waters; even in the arctic seas
there are fish. Some kinds swim near
the surface, others far below. It is es-
timated that at present there are about

Tail fin

Fig. 45 Which characteris-
tics of fishes does this gold-
fish have';' Where are the
gills? How many fins has the
goldfish?

Anal fin

PROBLEM I. The Kinds of Animals of the Earth

Fig. 46 Fish move by means of the muscular tail to which the broad tail fin is attached.
They have other fins, both paired and unpaired, which are used principally for
balancing, (new york zoological society)

two and a quarter billion people in
the world. But that is a tiny number
compared to fish populations. Of the
herring, alone, man catches and kills
about eleven billion each year. It has
been estimated that 200 billion other
herring are eaten annually by larger fish.
Yet the ocean remains well stocked with
herring. Twelve thousand different spe-
cies of fish have been described. They
range in size from the large tuna fish,
which weighs three quarters of a ton,
to the guppy of your aquarium which
measures a scant inch and weighs so
little you could not feel its weight in
your hand.

Some interesting fish. The flatfish,
that is, the flounders and the soles, are
curiously built. They are extraordinarily
flat from side to side and spend most
of their time lying on one side half
buried in the sand. Both eyes are on
one side, the side which is always up.
In the young fish the eyes are where you
would expect them to be, one on each
side of the head. Then one eye moves
around and joins its mate.

You may have heard of "flying fish,"

but fish cannot really fly. All fish, when
swimming rapidly, push themselves
through the water entirely by means of
their muscular tails. When near the sur-
face this motion of the tail may drive
them out of the water, so that fish are
often seen jumping. The flying fish have
very long paired fins which they spread
as they jump. Thus, they glide through
the air. Among the strangest fish are
those that can breathe by means of
lungs. They also have gills. Plan to do
Exercise 13.

Fish migration. Fish migrations are as
interesting and as puzzling as are bird
migrations and, naturally, much more
difficult to study. Although eels had
been known and caught as a food fish
for thousands of years, until about
thirty-five years ago no one knew where
they laid their eggs or where the young
grew to be adults. Each fall thousands
of mature eels were seen to swim down
the fresh water streams of Europe and
America into the Atlantic Ocean. There
they disappeared. Finally a scientific
expedition tracked them to a region east
of the Bermuda Islands where they lay

34 rbe Living Things of the Earth unit i

their eggs in deep waters. Then the streams. Here the eggs are laid. Then

parents die. The voting fish remain for most of the parents die. The young

a year near where the eggs hatch. Then develop slowly and eventuallv^ swim out

they begin the long journey to homes to the sea, where they remain until they

they have never seen in the rivers of the are ready for spaw ning. Within the last

two continents. The American eels turn few years much has been learned by

toward the rivers of our country; their the United States Bureau of Fisheries

European cousins travel eastward. When about the migrations of fish. Thousands

they are mature, they swim back to the of fish are tagged and fishermen are

breeding grounds in the Atlantic Ocean, asked to return the tag with information

The salmon, \\'hich live in the ocean as to the size of the fish and the place

when adult, migrate into fresh water at where it was caught. Fish are interestinq^

spaivn'mg (egg-laying) time. They swim to read about; see the bibliography at

far up into the shallow headwaters of the end of the book.

Questions

1. Into what five subdivisions or classes can the vertebrates be divided.'
What two or three characteristics do all vertebrates have?

2. Starting with the largest group, the phvlum, list the subdivisions em-
ployed by biologists in classifying animals.

3. In what two respects do mammals difi^er from all the other kinds of
vertebrates? Why may they be spoken of as the highest animals?
How many species of mammals are known to scientists?

4. Which mammals are most like man in structure?

5. List nine kinds of mammals that m.ay be grouped together as plant
eaters v ith grinding teeth. What is another characteristic of most of
these mammals? Explain.

6. What are the characteristics of the carnivores? List some carnivores.

7. Give the name of the gnawing mammals. What can you tell about
the gnawing teeth?

8. Give two reasons why a whale is classified as a mammal. State two
interesting facts about whales. What other mammals inhabit the sea?
Why are they classified with dogs or cats rather than with whales?

9. Tell what you know about bats.

10. What are the characteristics of marsupials? Where do most of them
live? Which animals in our countrv are closely related to the Aus-
tralian kangaroo? Why is the duckbill called a mammal? List two
unusual characteristics of the duckbill.

11. By which one characteristic can you always recognize a bird? What
are other characteristics of a bird?

12. How are birds classified?

13. Describe and give examples of birds of prey. In general, are they
useful or harmful to man? ]■ Apia in.

PROBLEM I. The Kinds of An'miah of the Earth 3<^

14. List some of the scratching birds. What do they eat?

15. List some wading birds. What are their characteristics? How do
swimming birds differ from wading birds?

16. Which is the largest hving bird? What are its peculiarities?

17. About how many species of perching birds are there? What is the
importance of these birds to man?

18. What can vou tell about bird migration as to: when birds migrate,
in which direction birds migrate in the various seasons, and how
far birds fly during migration. What problems in regard to migration
are still unsolved?

19. Explain how birds can fly. List three characteristics which enable
birds to fly. How does soaring differ from flying?

20. B\' which characteristics do you recognize reptiles? When an animal
is called cold-blooded, what really is meant? Where are reptiles most
common? Define hibernation. Into what three main groups (orders)
are they divided?

21. What are the four kinds of poisonous snakes found in this country?
Tell some facts about each of them.

22. State the peculiarities of structure in snakes. Explain how they carry
on locomotion and how they feed.

23. Tell something about the important snakes of other countries.

24. Describe how lizards resemble and diff^er from snakes. Which is the
only poisonous lizard in our country?

25. Why may alligators and crocodiles be dangerous to man?

26. Why are turtles called reptiles? What do they use as food and how
are they fitted for getting this food? Of what importance are they
to man?

27. What are the striking characteristics of amphibians?

28. Into what two groups (orders) are amphibians divided? Give an ex-
ample of each order. Compare the tailed amphibians with lizards.

29. Discuss the habits of frogs and toads. Of what importance are toads
to man?

30. State how you distinguish fish from other vertebrates. How do gills
differ from lungs?

31. How do sharks differ from true fish?

32. How numerous are fish as compared to land living vertebrates? How
do fish vary in size and appearance?

33. Describe the migration of eels and salmon.

Exercises

Mammals
I. Collect pictures of mammals and group them according to order
on charts or in a looseleaf notebook.

36 The Living Things of the Earth unit i

2. If possible, visit a zoo or natural history museum. Gather facts of
interest about several different kinds of mammals. To which order does
each belong?

3. Prepare special reports on topics such as the following: (a) The in-
telligence of the great apes, (b) the mammals of a special region, such
as Australia, (c) the mammals of my vicinity, (d) man's use of mammals.

4. When you have finished the section on mammals, gather together all
the important ideas you have learned about mammals under the following
headings: a list of mammals with those of one order gathered together;
the uses of mammals to man; the harm done to man by other mammals;
unusual mammals; mistaken ideas or superstitions about mammals.

Birds

5. Study of a living bird. If possible, observe a canary, a pigeon or a
chicken. Or study a house sparrow or some other common bird, out of
doors. How long is the bird? If you can handle it, find out how large
the bird's body is and how wide a wingspread it has. What markings
does it have? Describe their location accurately. (Make use of the dia-
gram in the text.) How far dow^n on the legs do the feathers go? In what
direction do the feathers on the wings and body point? Where are the
longest feathers? the shortest? Describe the toes. Examine the eyes
closely. Describe. How far around can the bird turn its head? Describe the
beak and method of getting food.

6. Have you ever looked closely at a feather? Cut the quill crosswise
to find out why it is so light. Use a hand lens for the study of the other
parts. Cut a point on the end of a large quill and use it as a pen.

Reptiles and Amphibians

7. Have you heard about the snake that swallows the end of its tail
and rolls like a hoop? Have you heard of the milk snake that steals milk
from the cow? Have you heard that horsehairs left in water Mill turn
into snakes? Comment on each of these statements. State: {a) What your
reason would lead you to believe and why, {b) whether in these cases
observation or experiment might help you arrive at the truth, {c) what
else you might do to convince yourself that each story is or is not true.

8. Are there poisonous snakes in your part of the country? Ask the
class secretary to write to the nearest college or zoo to find our. What
are they? Where are they likely to be found? How can you avoid being
bitten?

9. Using the facts presented in this book, write a brief report on the
importance of reptiles and amphibians to man. Add more information if
you arc sure it has been obtained on good authority. State what authori-
ties you consulted so that others can decide whether or not to accept the
information.

PROBLEM I. The Kinds of An'mials of the Earth ^y

Fishes

10. Study of a living fish. Examine a goldfish in a bowl of clear water.
Where are the paired fins; the unpaired fins? Examine and describe a
fin which is spread out. How are the scales arranged? Is this of any ad-
vantage to the fish? Try to catch the fish with your hand. What do you
notice? Describe the movement of the gill cover. What do you see under-
neath it when it is raised?

1 1 . State at least four ways in which the structure of a goldfish makes
possible rapid movement through the water.

12. Stir the water in the goldfish bowl to make the fish swim quickly.
What part of the fish pushes it forward? What part do the paired fins
play in locomotion?

13. Organize a class trip to a fish market on a Thursday afternoon
after school. List the kinds of fish. Take notes on their sizes, colors, and
markings so that you can recognize them again. How much do they
cost per pound? Compare the price with that of lamb, chicken, beef,
and pork. Why can fish usually be sold more cheaply than meat?

Further Activities in Biology

Ma7fmtals

1. Make plaster casts of the tracks of mammals. (See Mann and Has-
tings, and others.) If you can get dogs, cats, rabbits, and white mice, you
can take their footprints by wetting their feet with ink and leading them
across sheets of wrapping paper.

2. Since the class Mammals is so large, you and your classmates might
organize committees to make a special study of the different orders. If
written reports are prepared, they could be organized into one large
account of the mammals.

3. Breed white mice, guinea pigs, or rabbits, so that live mammals are
available for study.

4. If you can, learn something about the habits of one of the follow-
ing: rabbit, woodchuck, chipmunk, squirrel, prairie dog, deer. If possible,
take "notes" with a camera.

Birds

5. If there is no Junior Audubon Society in your school, ask the class
secretary to write to the National Association of Audubon Societies, 1000
Fifth Avenue, New York City, for further information.

6. Are you a Scout? Have you earned the Bird Study Merit Badge?

7. Even if you live in a city, it will be easy for you to keep and breed
pigeons on the roof.

8. Write to the Geological Survey, Washington, D.C., about bird-
banding. Read the National Geographic Magazine, January, 1928. Report
to the class on the subject.

The Living Things of the Earth unit i

Bird

Month 1

JAN.

FEB.

MAR.

APR.

MAY

JUN.

JUL.

AUG.

SEPT.

OCT.

NOV.

DEC.

Baltimore oriole

(

Bluebird

r ■

Blue jay

•

Junco

Ill

Red-breasted nuthatch

1 1

Fig. 47 A bird calevdar for Boston, Massachtisetts. Which bird stays the year round?
Which leave Boston in the fall? In the spring? See Exercise 13.

9. Can you get birds to stay in your neighborhood? Establish winter
feedinCT stations. See National Association Audubon Societies leaflets; or
A. A. Allen, Book of Bird Life.

10. If you are good at making things with your hands, build bird
houses and bird baths. You will enjoy watching the birds use them. See
L. H. Baxter, Boy Bird-House Architecture.

11. Do you know any birds by their calls or songs? Some of them are
very easy to recognize. Get phonograph records of bird songs to play in
the classroom. Records can be purchased from the Laboratory of Orni-
thology, Cornell University, Ithaca, New York. In some cities these rec-
ords can be rented from The Audubon Society.

12. Make a collection of deserted bird nests and show them to the class.
How many different kinds of materials go into the making of these nests?
(Do not collect nests still in use.)

13. When you have learned to recognize man\' kinds of birds you will
enjoy making a "bird census." List all the birds found in your locality.
Examine Figure 47. It \\'ould be interesting for you to prepare a bird
calendar for your part of the country.

14. Bird photography is a fascinating hobby. Much information can be
obtained from the camera department of Nature Magazine and magazines
on camping, hunting, and fishing. The finest achievement is a series of
pictures showing the life of the bird from egg to adult.

Reptiles and Ainplnbians

15. A terrarium (glass) may be set up for salamanders, newts, and
frogs. Mosses and small ferns M'ill help to make a forest floor.

16. Can you plan an experiment to discover the efl'ects of changes in
temperature on cold-blooded animals like the snakes and lizards? Use ice
and warm water but do not wet the animal. Why must )'ou change the
temperature slowly?

PROBLEM I. The Kinds o^' Ani'inals of the Earth

17. Report on the best treatment for snake bites.

18. Frogs and toads make excellent subjects for night photography.
Use a flashhght to find them, open the lens of your camera, and then
burn a photoflash bulb. The flash lasts about one fiftieth of a second.
The lens is closed afterward.

Fishes

19. Use a natural history such as Hegner's Parade of the AiYmial King-
dovi or copies of the National Geographic Magazijie to learn more about
fish and their relatives, the sharks. Prepare a short talk.

20. Have you ever maintained an aquarium of tropical fish? If you
have, report briefly to your class on their structure and habits. Could
you start an aquarium?

21. Look up lungfish. Tell your classmates why biologists consider
them important.

The Invertebrates

Animals without backbones. You know
that invertebrates have no backbone.
Whatever skeleton they may possess is
either on the outside, like a coat of
armor, or is so different from the skele-
ton of the backboned animals that you
M^ould never confuse the two. And while
all vertebrates are assigned to a single
phylum the kinds of invertebrates are
so varied that they are arranged in dif-
ferent phyla. Zoologists are not all in
agreement on just how many phyla the
invertebrates should be divided into.
However, all classifications include the
nine important phyla we will study. In
the diagram on page 40 there are draw-
ings of one representative of each of
these nine phyla. From the many thou-
sands of possible kinds these nine were
chosen: a grasshopper, a snail, a starfish,
an earthworm, a hookworm, a planaria
(a relative of the tapeworm), a jellyfish,
a sponge, and an ameba. In this book only

a very few of the thousands of species
of invertebrates can be described. There
are about 800,000 species of inverte-
brates in contrast with the 40,000 species
of vertebrates.

Fig. 48 This circle graph will help you com-
pare the mmibers of species of invertebrates and
vertebrates. It will also help compare the num-
ber of species of insects with the total mimber
of all other kinds of invertebrates. There are
approximately 40,000 species of vertebrates and
800,000 species of invertebrates, of which 600,000
are insects.

The Liv'mg Thmgs of the Earth unit i

ARTHROPODS

Grasshopper

MOLLUSKS

ECHINODERMS

Snail

Starfish

ANNELIDS

NEMATHELMINTHS

PLATYHELMINTHS

Earfh

worm

Hookworm — Roundworm

Planaria — Flatworm

COELENTERATES

SPONGE ANIMALS

PROTOZOA

Jellyfish

Fresh water Sponge ^^ Ameba

Fig. 49 The invertebrates are classified by zoologists into mmierous phyla. One vtem-
ber of each of the nine principal phyla is illustrated above. Do you know other
members of these phyla?

PROBLEM I. The Khids of Ajiiffials of the Earth

Fig. 50 These are representatives of each of the five principal groups of the Arthro-
pod Phylum. Which cormnon afiinial is an example of each group':'

PHYLUM - ARTHROPODS

Jointed-Legged Invertebrates

A glance at the arthropods. The in-
vertebrates with jointed legs, or ar-
thropods, are the most complex inverte-
brates. You can recognize an arthropod
by two characteristics: they have jointed
legs and they have an external (outside)
skeleton made not of bone or cartilage,
but largely of a material called chitin
(ky'tin). Most of the arthropods can
be classified in five groups or classes.
Examples of these five classes are repre-
sented in Figure 50: the insects, the
spiders, the hundred-leggers, the thou-
sand-leggers, and the crustaceans (crus-
tay 'shuns) which include crabs and
lobsters.

What is an insect? Let us begin our
study with the most common arthro-
pods, the "insects. Insects differ from the
other arthropods in that they have six
legs and three distinct body parts: a
head with feelers called anteTi?iae (an-
ten'nee), a thorax with three pairs of
legs, and an abdomen (ab-doh'men).
The abdomen never has legs. In the ab-
domen you can see distinct rings called

seginents. Most insects have two pairs
of wings, but you cannot depend on
this as a way of recognizing insects, since
some insects have only one pair and
others have no wings at all. The wings,
legs, and feelers are called appendages
(ap-pend'a-jes). If you examine Figure
59 and the other pictures of insects, you
will see the parts mentioned here.

Most insects have large eyes, called
compound eyes because each eye con-
sists of many six-sided lenses. Insects
can hear, too. Some have eardrums; some
seem to use the feelers as organs of
hearing. But the feelers seem to serve
also as organs of smell and touch.

Insect flight is very different from bird
flight. In most insects the wings move
with astonishing speed. The house fly's
beat is about 3 30 times a second. You can
understand why it makes a buzz. How-
ever, the speed is not the same in all in-
sects. The grasshopper has been timed at
twenty miles an hour. The "darning
needle" can fly at the rate of sixty miles
an hour but no insect flies far without
stopping.

The life story of an insect. Let us trace
the life story of a common insect, a

The Living Things of the Earth unit i

Fig. 51 Three stages hi the developvient of the monarch or vtUkiveed butterfly are
show7i. The changing-over stage {pupa stage) is called the chrysalis. It has a bard coat.
Which stage is not illustrated? (American museum of natural history)

butrerflv or moth. The eggs laid by the
parent develop into wormlike creatures
called caterpillars. A caterpillar does
not look at all like an insect; it certainly
lacks the three-part division of the body
and seems to have more than the typical
number of legs, it has no wings and no
feelers. After a period of steady feeding-
it either forms a hard protective coat or
builds a little house around itself. If
the little house is spun, it is called a
cocoon (kuh-koon'). Many changes oc-
cur within the cocoon and after some
time the insect conies our a full-grown
butterfly or moth. These insects, there-

changing-over stage, called the pupa
(pew'pa); and the adult. This compli-
cated life histor\' is referred to as a
co7f7plete metamorphosis (change).
Many other insects have these four
stages in their life history. All the ants,
bees, wasps, flies, mosquitoes and beetles
have complete metamorphosis.

There are other insects, the grasshop-
per for example, that lack a pupa stage.
In these there arc only three stages: the
^^^■, the nymph which is much like the
parents, and the adult. This kind of life
history is called hicojjiplete vietavwr-
phosis. If N'ou are interested in insects

fore, go through four stajres: the ^^J^^\ you will want to do some of the things
the caterpillar, called the larva; the suggested on pages 68-70.

PROBLEM I. The Kinds oj Aiiiviah oj the Earth

Fig. 52 Silkworm moth. Adult (top), e^iipty
cocoons (center), larva (bottom). The adults
lay eggs ivbicb batch into larvae. Each larva
spins a cocoon of 2400 to ^600 feet of silk fiber.
Do you know what the larvae eat and how silk
thread is made from the cocoons? (American

MUSEUM OF NATURAL HISTORY)

Insects with scaly wings. This group
includes moths and butterflies. These
insects have large wings covered with
tiny scales. The scales are often brightly
colored and in some species are arranged
in gay patterns. They are loosely at-
tached, as you know if you have ever
handled a butterfly or moth. If you use
a microscope you can see that the
"powder" that comes ofi" the wing con-
sists of these scales. The bodies of moths
have much more "hair" on them than
have those of butterflies; their bodies

Fig. 54 Coiled sucking tube of a moth, (gen-
eral BIOLOGICAL supply)

are also heavier and often more clumsy.

Butterflies and moths suck nectar (a
sugary liquid) from flowers. The mouth
parts form a tube, sometimes a very long
tube, w hich is kept coiled up when not
in use as illustrated in Figure 54. When
extended some tubes Mill reach the nectar
bags at the bottom of deep flowers.

The feelers or antennae of moths are
feather-like, while those of the butterfly
are smooth and sometimes knobbed at the
tip. If you watch moths and butterflies
when they alight you will detect yet

The Living Things of the Earth unit i

Fig. 55 (left) Have you ever
seen the tongue of a housefly
inovhig up and down as it
lapped its food? (American

MUSEUM OF NATURAL HIS-
TORY)

Fig. 56 (below) The Hes-
sian fly ijipires wheat. Its lar-
vae Slick the sap from tender
parts of the stem. Can you
find the halters that take the
place of the second pair of

Labium
(outer lip)

Skin surface

Proboscis

(piercing mouth parts)

Fig. 57 (left) The mosquito keeps its piercing
moutl? parts in a sheath when not in use. The
mouth parts forni a tube through which blood
is pumped from the victim. (American museum

OF NATURAL HISTORY)

another difference: moths spread their
wings flat when resting; butterflies hold
thcni upright.

The two-winged insects — flies. The
members of this group have onlv one
pair of wings. There are stumps in

PROBLEM I. The Kinds oj Animals oj the Earth

Fig. 58 A praying 7na7itts
finishing her nest. How does
the praying ?}iantis resemble
the grasshopper? How is it
different? (selena johnson)

place of a second pair. They have mouth
parts of various kinds. Some lap up their
food, some chew, while others can only
suck. Common examples of this order
are the familiar housefly and the tiny
fruit fly- Small flies do not become large
flies. Increase in size occurs only in the
larval stage, and the larva of the fly is
a wormlike creature without wings or
legs, called a maggot. The mosquitoes,
gnats, and midges belong to this order,
too.

Grasshoppers and their relatives. Be-
cause it is large, the grasshopper is a
good insect to examine more closely.
Grasshoppers are also called locusts,
especially in Europe and Asia. It is likely
that the locusts of Biblical times were
grasshoppers. See Exercises i and 2.
The grasshopper group (order) includes
among others the crickets, katydids,
cockroaches, and the praying mantes.
Ferocious as the praying mantis looks
it will do you no harm. It is the grass-
hopper that may well be afraid, for off
comes its head if the mantis catches it.

tenno

— Labial palpus

Meta-meso-pro-
fhorax

Fig. 59 In a grasshopper one can easily see head,
thorax, and abdomen. How many segments do
you see in the abdomen? The appendages of the
right side are shown. How inany are there of
each kind? The hind wrings fold up like a fan.
What ?mght be the use of the front wings?

Grasshoppers are equipped with exceed-
ingly muscular hind legs. A grasshopper
is capable of a standing broad jump
fifty times the length of its body, while
man's latest Olympic record is only
about twice his length! One grasshopper

The

can do liitle harm. But scmerimes in our
western states, and in other parts of the
world, they occur in vast numbers and
may strip fields of everything green.
Crops of wheat or corn or even fruit
trees may oe ruined within a few hours.

Blips. All small insects and even disease
^erms are called "bugs" by many people.
The name bugs, however, is properly
applied onU' to one group of insects. It
is a group with which, for the most
part, you do not want to have much
to do. It includes amongr many others the
fleas and bedbugs. The lice which live-
on birds and mammals are closely related
to the bugs. Of course, there are many
bugs that do not live on other animals.
Some live in the water striding over the
surface or swimming near the top.

Closely related to the true bugs, al-
though belonging to a different order,
are the plant lice and the scale insects.
The plant lice, or aphids, are soft-bodied
insects which cling tightly to plants and
suck their juices, weakening the plant and
often killing it. The scale insects attack
many kinds of trees and shrubs. Like
aphids they multiply into millions. They
cover themselves with tiny scales like
shields; thus protected, they feed on the
sap.

Beetles. All beetles have hard wing
covers which completely cover the up-
per side of the abdomen and fit so
closely that you can scarcely see the
seam down the middle of the back.
The ladybird beetle made famous by
"ladybug, ladybug, fly away home" is
common even in cities; and the Colorado
potato beetle is often found in the po-
tato patch. Another common beetle is
the firefly whose light goes on and off

Living Things of the Earth unit i

Fig. 6o The Colorado potato beetle does Tinicb
dajnage. How do you know it is a beetle? (u. s.

DEPARTMENT OF AGRICULTURE)

like a tiny flashlight as frequently as
once every second or even faster, and
sometimes with great regularity. Its light
is located on the lower side of the ab-
domen. In the larva stage they are called
glowworms and can be found shining in
the grass. If you can collect half a tum-
blerful of glowworms you will have
enough light to read by.

Insect communities. Most insects live
quite solitary lives, but ants, most bees
and wasps, and the "white ants" or
termites live in large communities. They
are the social insects. Each insect per-
forms some special job which benefits
the whole community.

Of all the social insects, the ants,
which are found in almost every part
of the world, are the easiest to study.
Most of you have had the experience of
discovering an ant nest beneath a rock.
You may have seen the ants pick up
large white bundles, run back and forth,
and finally dash off to some safe hiding
place. Then they come back for more
bundles until shortly the nest has been

PROBLEM I. The Khids of Ajii7Jials of the Earth

Fig. 6 1 Apbids (plant lice) and ants on a steni.
The apbids produce a sweet liquid (hojieydew)
which the ants like, (hugh spencer)

cleared out. You may have heard these
bundles called ant eggs, but they are
much too large to be eggs; they are the
pupae. Most of you, too, have seen in
fields, or at the edge of the forest,
mounds of earth with many ants scur-
rying about. These anthills may be two
or three feet in diameter and may house
several thousand insects.

Underground, in the dark, passage-
ways are tunneled; chambers of many
kinds are dug out. There is much rush-
ing to and fro with bits of food or soil.
All this work is done by the workers.
Every nest houses many workers, thou-
sands of them, and one much larger ant
known as the quee?i, a female who does
nothing except lay eggs. Sometimes,
there are ^several queens in one nest. And
there are, too, a very small number of
male ants that do no work. But the vast
majority are workers. Some workers de-
vote themselves to the care of the young.
All the feeding of larvae and the moving
about of larvae or pupae from room to
room is done by the workers.

Fig. 6i An aJit tejiding a mealy bug. Mealy
bugs are relatives of the apbids. J hey also tnake
honey dew. (amer7can can co.)

Winged female

Female minus wings
(queen)

Workers

Fig. 63 The life history of the little black ant.
How many kinds of adults are there? What
does each do?

Among some species of ants there
are Morkers that biologists have called
soldiers because they have very large
biting jaws and apparently devote them-
selves to defending the rest of the com-
munity within the nest. Some warlike
species even raid the nests of other ants.
Among other less warlike species the
workers make mold gardens and raise
aphids. See Figures 61 and 62.

The Living Things of the Earth ' unit i

The life of the bee. Bumblebees are
the giants among bees. They live in
fairU' small colonics in the ground.
Honeybees live in nuicii larger com-
munities than do bumblebees; each col-
ony ma\' consist of more than 35,000
individuals. They build their nests in
caves or hollow trees or in beehives
provided by man. These are the bees
that make the honey of commerce.

Fig. 65 (above) From left to right these are
worker, drone {male), and queen (jemale)
bees. How can you tell one fro?n the other?
(root)

Fig. 66 (left) A swarm of bees. How does the
beekeeper take advaiitage of swarming to start
a new hive? How many bees would you judge
to be in this swarm? (u. s. bureau of ento-
mology)

There are males, females, and worker
bees. See Figure 65. As among ants, the
queen is the central figure in the com-
munity. She is fed and carefully guarded.
She lays eggs, thousands of them, while
the workers toil. They build the honey-
comb of wax which forms from a
liquid which oozes out of their bodies.
They cut the wax into plates with their
jaws and build the amazingly exact six-
sided chambers. When these rooms are
completed the queen deposits one tg^
in each. Other workers bring in food.
Flying from flower to flower they gather
nectar, a sweet liquid which they store
temporarily in a special honey stomach.
When they return to the hive they give
it up again to feed to the young. Or
they change it into thick hone\' and
store it in the honc\'comb. When a
cell of the comb is filled with honc\- they
cap it with wax. Often they gather pol-
len from flowers. This they prepare

PROBLEM I. The Kinds of Anbuah of the Earth

into special food which is fed to a few-
larvae which develop into queen bees.
In the meantime, they do much cleaning
of the hive. The workers also meet the
attacks of "robber" bees and other ani-
mals. For this, the bee uses the sting on
the end of its abdomen.

Most of the thousands of individuals
in a honeybee colony are workers. The
life of a worker may be only several
weeks or at most several months, but the
colony increases in number rapidly be-
cause of the rapid rate of reproduction.
From egg through larva and pupa stages
requires only three weeks. Whether be-
cause of the crowding or for some
other reason, in the early spring and
summer large numbers of bees together
with the old queen bee leave the hive
in a mass and start another colony. This
is called swarming. One of the young
queens that remains takes over the egg-
laying duties in the old colony.

For centuries man has domesticated
bees for the sale of their honey and their
wax, but bees have never been tamed.
However, they will sting only when
disturbed and frightened, injecting poi-
son with the sting which is left in the
wound.

Insects that eat wood. The community
life of the so-called "white ant," prop-
erly named termite., is just as interesting
as that of bees or ants. Termites live
mostly in the tropics but are spreading
through the temperate zone where some
of you may have become better ac-
quainted with them. They burrow and
build in wood, sometimes wrecking
houses or other largre wooden structures.
Working in the dark, well concealed in
the timbers, their presence in a building

i '

\ iH

1^^

3
^

r^l

^^^

1^%^ ^i^m

Fig. 67 A beam of wood almost completely de-
stroyed by termites. What can be done to pre-
vent damage to wood by termites? (science
service)

is sometimes not suspected until some
day, when the framework has been
weakened, the whole structure collapses.
Sometimes, however, they are detected
when they swarm in the spring. In warm
climates or even in cooler climates where
buildings are constantly kept warm,
termites are a real danger. We can pro-
tect ourselves against them by soaking
the timbers in creosote or, better still,
by using concrete for foundations and
lower floors of buildings. This is effec-
tive because termites must have at least
a portion of their nest in moist soil or
wood.

How insects make a noise. In the sum-
mer there is a steady chorus of crickets
chirping. As it gets hot the male cicadas
or "seventeen-year-locusts" add their
loud, shrill song. When night comes on
the katydids call from every tree, arguing
endlessly, "Katy-did, Katy-didn't." It is
so noisy that many a city dweller has

The Living Things of the Earth unit

Fui. 68 The black widow
spider 7J?agnified. ]Vith legs
stretched otit it is ctbout one
and one half inches in size.
The lower side of the abdo-
men with its distinct hour-
glass is shown at the nppcr
right. At the lower right cor-
ner is the body of the n/ale.
How does it compare in
size with the female';' (v. s.

DEPARTMENT OF AGRICULTURE )

w (jndered what was meant by the "quiet"
of the countryside.

The sound-producing apparatus of the
cricket is peculiar. The front pair of
wings is thickened. The edges of the wing
covers have a set of "teeth." As one roug^h
surface rubs over the other the stiff winos
vibrate. It is the vibration that is heard as
a shrill chirping. In katydids and cicadas
the apparatus is slightly different. In these
insects it is only the males that are so
equipped. Other insects, such as bees and
flies, make noise by the rapid beating of
their w inos.

The insects. So numerous and so varied
are the insects that many books have
been filled with accounts of their extraor-
dinary structure and fascinating lives.
This brief account has onlv scratched
the surface. Tlie biologists who study
insects (called entomologists, en-toh-
niol'o-jists) can tell man\' excitinu^ tales
of the doings in the highh' populated

insect world. For review do Exer-
cise 3.

Other arthropods — the spiders. If you
turn again to the chart on page 41 vou
will see that besides the very laroe and
varied class of insects there are three
other classes in the arthropod phylum.
One of them is the spiders and their close
relativ^es. Does it astonish you to learn
that spiders arc not insects? It should
not. Being arthropods, of course, they
have a firm outer covering and jointed
legs; but ^'ou \x\\\ count four pairs of
legs (not three), and only two body
parts. The head and thorax are joined
together. And x\\q\ lack three structures
found in insects: ^ings, antennae, and
compound eyes. Now draw the diagram
suggested in Exercise 4.

Most spiders can give off a special
]i(]uid from the abdomen that hardens
in riic air into a silk thread. The webs
nv,i\ be used as homes or as a means of

PROBLEM I . The Kinds of An'mials of the Earth

Fig. 69 The garden spider spins an orb zveb of
this kind. It rests motionless in the center.
(HUGH DAvas)

Fig. 70 The bite of the tarantula is rarely fatal.
Hoiv do you know it is a spider? (u. s. bureau
OF entomology)

catching prev. The house spider spins
a tangled mass of threads in some quiet
corner; this is a cobweb. Each species
has its own characteristic web and many
webs are comphcated structures woven
according to a definite pattern. The
trapdoor spider digs a hole in the
ground and covers it with a door open-
ing out\\'ard on a hinge.

Do spiders bite? The fear of spiders
like the fear of snakes is the result of
ignorance. Most garden spiders do not
bite; or if thev do the bite causes no
more than a slight irritation. The com-
mon house spider does not bite at all.
The only dangerous spiders in the
United States are the tarantula and the
black widow or hourglass spider (see
Fig. 68). The black widow thrives best
in the tropics, but has been found in

many parts of this country. It is eas\'
to identify for it has a black body with
a red spot shaped like an hourglass on
the under side of the abdomen.

Close relatives of the spiders. The
scorpion is a close relative of the spider,
though you might not recognize it as
one. The scorpions of this country can-
not do much harm. But in the tropics,
where they may be as much as eight
inches long, they may be dangerous.
Then there are the tiny mites and ticks.
Many of them live on, or just under, the
skin of various mammals, including man.
Some of them, like the chigger, cause
fierce itchinsrs. Some are carriers of
dangerous disease germs. Another rela-
tive of the spider is the harvestman. You
may know it as daddy longlegs, from
its unusually long and spindling legs.

The Living Things of the Earth unit i

Fig. 71 The house centipede enlarged. How do
you know that this is not a niillipede? (u. s,

DEPARTMENT OF AGRICULTURE)

The hundred- and thousand-legged
arthropods. A glance at the chart on
page 41 will show you members of two
more classes of arthropods, the "hundred-
leggers" and the "thousand-leggers."
Their bodies are made up of a series
of rings; that is why many persons think
that they are worms. But they have
jointed legs attached to each ring, and
their bodies have a firm covering. The
hundred-leggers or centipedes, have a
pair of legs on each ring. The thousand-
leggers, or millipedes, have two pairs
of rather short legs to a ring. Both these
classes are small and rather unimportant.

The crustaceans. Another great ar-
thropod class, the crustaceans, includes
many forms that inhabit the sea, but
some live on land and some in fresh
water.

It is difficult to state by what charac-
teristics you can recognize crustaceans.
About all that can be said here is that
if an animal seems to be an arthropod
and does not exactly fit into the insect,
spider, or centipede groups, it is prob-

FiG. 72 Rock barnacles. These are crustaceans.
Almost 3000 of them have been counted on one
square foot of rock, (morris)

ably a crustacean. The class includes the
lobsters and crabs, the crayfish, water
fleas, barnacles, shrimps, and hundreds
of other kinds. Study some crustacean at
first hand as described in Exercise 5.

Some queer crustaceans. Perhaps all
crustaceans deserv'e to be called queer.
The lobster is just an ordinary kind of
crustacean; but it has eyes that are on
the ends of stalks, huge and powerful
pincers or claws, and it glues its eggs to
its legs. In spite of the saying "as red as
a lobster," live lobsters are not red at
all; only cooked lobsters are red.

The crab, too, has eyes on stalks.
Its body is wider than long, and it seems
to have no abdomen. The queerest thing
about the crab is its walk. It walks side-
ways, but it manages pretty well. And
in the water it is a good swimmer. Along
the coast you can often buy soft-shelled
crabs. These are common crabs that
have recently lost their shells. All the
crustaceans with hard coverings shed
their coverings as their bodies become
too large for the shells.

PROBLEM I. The Kinds oj AnmiaJs 0^ the Earth

Fig. 73 Lobster catchmg a [^
crab. Both are crustaceans.
How can you distinguish
lobsters jrorn crabs? (Ameri-
can MUSEUM OF NATURAL

history)

Fig. 74 The scorpion is

grouped with spiders, al-
though it looks quite differ-
ent. It carries its young on
its back. The sting at the
end of its abdoinen can be
waved over its head. (Ameri-
can MUSEUM OF NATURAL

history)

For strangeness, the barnacles take the
prize. It was a long time before thev
were recognized as relatives of lobsters
and crabs. A famous English biologist,
T. H. Huxley, has given this striking
description: "A barnacle may be said
to be a crustacean fixed by its head and
kicking the food into its mouth with its
legs."

Exercises 6 and 7 would be good re-
view exercises before you leave the
group of jointed-legged invertebrates.
You will next examine briefly eight other
invertebrate phyla. We shall proceed
from the more complex to the more
simple forms.

PHYLUM - MOLLUSKS

The Soft-bodied Invertebrates

What are mollusks? If you examine
Figs. 75-78 you will see examples of
three different groups (classes) of mol-
lusks: those that have a foot which is
used in creeping, like the snail; those
that have feet used in seizing prey, like
the octopus; and those that have a
hatchet foot used in plowing through
wet sand or mud, like the clams. Most
have a shell of lime which protects
the soft body. The shell takes very dif-
ferent forms; it may be single or double
and may even be carried internally.

The Living Things of the Earth unit t

Fig. 75 (above) The octopjis is a iiiollusk irhich
has 710 shell. Its eight ivaving tentacles {or feet)
hear sucking cups. With feet and beak it tears
its prey to pieces, (new york aquarium)

Fig. 76 (right) This zebra snail is creeping on
its foot. (I)AVIS)

Clams, oysters, and mussels. These
mollusks have a shell in two parts. Often
the shell is left open and the hatchet
foot, a thick muscle, may stick out.
Oysters and mussels, which spend their
lives attached to rocks or other shells,
have so small a foot that they can hardly
be said to have one. Clams use their foot
for locomotion. Exercise 8 is interesting
althouoh difficult.

Snails with and without shells. Snails
live in water and on land. Land-living

forms especially have a well-developed
foot. They have a well-developed head
too, with a real mouth, and eyes carried
on long stalks. Many species carry a
spiral shell from which the head and
foot protrude. When danger threatens,
both head and foot arc drawn into the
shell and the tough, slimy foot seals
the mouth of the shell so \\ell that it is
difficult to extract the animal. Snails that
lack a shell are called slugs. They may
do much damage in the vegetable garden.

PROBLEM I. The Kinds of An'wials of the Earth

Fig. 77 Although the slug is a molUtsk, belong-
ing to the same group as the snail, it has no
shell. This one has just laid its eggs on a leaf.

(MARY C. DICKERSON)

Fig. 78 The clain has a double shell and a
hatchet foot. The claifis above a7-e using the
foot to ploiv through the sand, (ward's natu-
ral SCIENCE ESTABLISHiMENT)

Mollusks and man. A great many spe-
cies of mollusks are eaten by man. Snails
are considered a delicacy by some people,
and the octopus and squid are eaten in
many parts of the world. Oysters, the
many species of clams, the scallops, and
the mussels are commonly eaten. Oysters
are valuable also as the source of mother-
of-pearl, from which buttons are made.
Precious pearls are found only in certain
tropical species and then rarely.

There are comparatively few kinds
of pests among mollusks. One of the
worst is the "shipworm." It bores into
timber which is under water, riddling
it with tunnels until the \\'ood collapses.
Now that ships are made of steel the
damage done by shipworms is confined
to wharves.

PHYLUM -ECHINODERAIS

Invertebrates ivith Spiny Skins

A different body plan. The inverte-
brates with spiny skins are called
Echinoderms (eh-kine'o-derms). They
are built on a plan different from that
found in the more complex animals.
Most animals have bilateral syimnetry.
This means that if they were cut down
the middle the two halves would be
about the same in appearance. But the
invertebrates with spiny skins have
radial synmtetry, like a wheel. Just as
the spokes of a wheel radiate from the
hub, so the parts of these animals radi-
ate from a central point. Besides this,
these animals have a spiny skin and a
complicated system of water vessels that

The L'w'mg Things of the Earth unit i

Fig. 79 The horny, rough tipper surface of a
C07HV1071 starfish. What kind of synnnetry has

it? (AMERICAN MUSEUM OF NATURAL HISTORY)

help in locomotion. Some of them are
brightly colored and are very beautiful
in structure.

If you live near the sea, you are surely
acquainted with starfish, sea urchins, and
perhaps sand dollars. In tropical waters
the beautiful sea lilies, which you might
well mistake for plants, grow attached
to the sea bottom. All of these are spiny-
skinned invertebrates.

The starfish. The starfish lives in salt
water near the shore. It is not a true fish,
of course. It is a living flexible star with
five arms and a spiny covering colored
brown or red or purple. Hundreds of
tiny tube feet with suction cups at
their ends dot the lower surface of the
animal. By pulling in and pushing out
the many tube feet in succession the
starfish moves along slowh' and
smoothly. These tube feet help in
breathing, too, and in food getting. By
folding itself over an oyster and at-

FiG. 80 The sea urchin has a beautifully marked
shell beneath these spines. (American museum

OF NATURAL HISTORY)

taching its tube feet it pulls the shell
open. Then it turns its stomach inside
out and digests the living oyster in its
shell.

Starfish do much damage by feeding
on mollusks. Oystermen formerly tried
to destroy starfish by tearing them in
half and throwing the pieces back into
the sea. Unfortunately, this made the
situation worse, for new parts similar
to those lost will grow back, or regen-
erate, making two animals where there
had been but one before.

Some starfish relatives. Similar to the
starfish group but sufficiently different
to be put in another class are the sea
urchins and sand dollars. They, too,
have their mouths on the lower side.
They take in sand, in which thev find
small animals and plants which arc their
food. The sand dollar has a circular
flattened shell somewhat thickened in
the middle. The sea urchin is so covered
with movable spines that it looks Hkc
a walking pincushion. Sea urchins are
eaten by some people; their large masses
of eggs are considered a great delicacy.

PROBLEM I. The Kinds oj An'wials oj the Earth 57

Oesophagus Crop Gizzard Intestine

Pharynx

Mouth Head ganglion Hearts Blood vessels Nerve chain of ganglia

Fig. 81 Front end of an earthworm cut open. The blood vessels, nerves, and many
other parts are similar to those of 7/;ore complex animals. See Figure 82, also.

Three Phyla of Worms

PHYLUM - ANNELIDS

Worjiis with Segments

Earthworms and their relatives. Perhaps
the most important of the Annehds
(ann''ell-ids) are the earthworms. You
will find them interesting to study.
See Exercise 9. Most of the time earth-
worms burrow underground where
they literally eat their way through the
earth, swallowing soil particles and de-
caying plant material, which is their
food. The food is used and the undi-
gested soil is left behind in little ropes
which hold together until they are dry.
You may have seen them on the ground;
they are called castings. Charles Darwin
and his sons studied the activities of the
earthworm with great care. They dis-
covered that the animal often brought
its castings to the surface and that,
therefore, on a small scale, earthworms
were constantly plowing and cultivating
the soil, making themselves useful to
man. If you look at Figure 81, you will
see that the body is made up of rings
or segments. All the M^orms in this
phylum are segmented. One fresh water

form that is rather common is the
leech. There are suckers at both ends
of the body which enable it to stick
tightly to the animal from which it
sucks blood; that is the origin of the
expression, "sticks like a leech." It has
teeth with which it breaks through the
skin and a substance in the saliva which
prevents the clotting of blood; thus it
can suck until it is full.

PHYLUM - NEMATHELMINTHS

Roimdworms

The hookworm and its relatives. There
are other Nemathelminths (nem-a-
thel'minths) but the hookworm is the
best known of this group. In later
chapters you will read more about them.
Hookworms and some other members of
this phylum live in the bodies of both
man and other animals where they may
cause disease. Most of the roundworms
are tiny, too small to be seen w ith the
naked eye. Their bodies have no seg-
ments. Thev are present in large num-
bers everywhere, particularly in the soil,

Fig. 82 An eartbwun/i burrowing in the soil.
It looks shiny because its skin is moist. (Schnei-
der AND SCHWAiaz)

Fic. 83

you see

( AMEUIC:

I'Lviiiria is less tl.HTii one inch long. Do
the exiling lube 'vehich it can extend?

AN MUSEUM or NAI UKAE HISTORY)

The L'tv'mg Things of the Earth unit i
PHYLUM - PLATYHELAIINTHS

F la fd: 011ns

Tapeworms and their relatives. The

phity helminths (pla-tee-hel'minths) in-
chide the tapeworms and the hver flukes,
both of whicli are parasites. Tapeworms
are flat like a ribbon, but it is a ribbon
made up of separate pieces which can be
dropped off one by one. Tapeworms may
reach a IcnjTth of twenty feet. Some
species live in man's intestines, hooked
to the wall bv the curved spikes and
suckers on their heads. Thev live on the
food which man has dii^ested. You will
read more about tapeworms later.

Other flatworms that are of great im-
portance to man because they attack him
or his domesticated animals are the liver
flukes. They are tiny worms that live in
the liver of sheep and other animals.
They do great damage. One very com-
mon flatworm, Planar ia (plan-air'ree-a),
lives in sluggish streams, hidden under
stones. Examine Figure 83. Although
Planaria is of no economic importance,
it has been studied and experimented
with by many zoologists.

PHYLUM - COELENTERATES

Aii'nnah Whose Bodies Are S'niiple Sacs

Sea anemones. The coelenterates (see-
len'ter-ates ) are of great interest to zo-
ologists but most of them are of little
economic importance. If you sec jraily
waving tentacles above a delicately tinted
body fastened to the sea bottom \on are
looking at a sea anemone (a-ncm'o-nce),
the "flower" of the ocean. Man\' are
blow 11 in color; some forms arc pini«; or
rose-colored; others are oranoc or bluish

PROBLEM I. The Kinds of Animals of the Earth

Fig. 84 Sea ane7nones. These beautiful animals are several inches high. Where do they
live? How do they get their food? (naturf. magazine)

green. The body is little more than a sac
in which food is digested. The mouth is
a slitlike opening in the upper end of the
sac; the tentacles that surround it grasp
the food which the water may wash
within reach. They can shoot out long
stinging hairs which paralyze or kill their
prey. Once the food is caught the ten-
tacles push it into the mouth. When the
tide goes out leaving the little anemone
in a rocky pool, it pulls in the tentacles
and contracts its body until it is nothing
but a small solid mound.

Related to the sea anemones is hydra,
a tiny fresh water form. You may have
found it attached to the sides of an aquar-
ium. See Figure 85.

Animals that make rock. Coral animals,
also, are attached to the sea bottoms.
They resemble sea anemones but differ in
several ways: they are usually much
smaller; they are attached to one another
in colonies; and they build shells of lime

Fig. 85 Hydra, cut open and magnified. This is
a tiny anmial, seldom more than one fourth
inch long. Look for the mouth surrou?ided by
tentacles. These have stinging cells which can
kill small aniffials.

Tentacles

Body cavity

Stinging cells

Spermory

Bud (will form
a new hydra)

Ovary

Part by which
Hydra attaches
itself

The Ltv'mg Things of the Earth unit i

Fig. 86 Organ-pipe coral. The tiny animal within each tube can extend brightly
colored tentacles. (American museum of natural history)

outside their bodies. There are many spe-
cies of coral animals. Each species con-
structs of shell of a particular kind.

Most corals inhabit the warm waters
of tropical seas in vast colonies contain-
ing thousands upon thousands of indi-
viduals. When each animal dies its skel-
eton remains behind; thus slowly but
steadily a mass of shells piles up. This
turns to stone — limestone. After long
ages so much rock gathers that a reef or
coral island may rise out of the water.
Reefs are sometimes a thousand miles or
more in length. The Bermudas are a
group of coral islands.

A third class — the jellyfish. Grownup
coral animals and sea anemones spend
most of their lives sittin<r down but in
their vounger stages thev can move
about. There are other forms, such as
the jellyfish, that never settle down. The
animal is realh' jcllvlike; clear, trans-

parent, and soft. The body of the jellv-
fish is more than 95 per cent water.
When washed up on the dry beach the
water soon evaporates away until just
a shriveled shadow remains.

Jellyfish look like inverted saucers
floating in .the water. See Figure 87.
They vary in size from about one inch in
diameter to several feet. The jellyfish
moves throuijh the water by wavintj its
tentacles or by contracting its body. The
contraction squeezes w^ater out of the
central cavity; this gives the jellyfish a
little push in the opposite direction.

Characteristics of the coclenterates.
The coclenterates are all water-dwelling
animals. Like the starfish thev have ra-
dial symmetry, but thc\^ are far simpler
in make-up. Each animal is much like a
simjilc sac. The sac has one opening
called the mouth which is surrounded
b\^ tentacles with stinging hairs.

PROBLEM I

The Kinds of An'nnals of the Earth 6 1

holes. Sponges grow fastened to the floor
of tropical seas from which they are torn
by dredges or cut loose by divers. After
they have been killed they are hung in
the air until the animals have decayed.
Then the sponge is washed in water until
nothing but the skeleton of the colony is
left.

PHYLUM - PROTOZOA

The First An'nnals

What are the protozoa? The nn\

masses of living matter making up the
bodies of all animals and plants are called
cells. The common animals and plants
you know are made of billions and bil-
lions of cells. But some animals and plants
are made of only a single cell. As you
would expect, such animals and plants
are tiny, usually so small that they can
be seen only by means of a microscope.
The group of one-celled animals is called
the Protozoa, which means "first" or sim-
plest animals.

Protozoa are found living in many dif-
ferent places. Ponds and streams are often
crowded with them, although the water
looks clear. Some parts of the ocean are
thronged with protozoa, as you will read.
There are protozoa that live in the intes-
tines of animals, and others that may live
in our blood and cause serious illness
(malaria). Altogether, they are as fasci-
nating a group of animals as we know\

Raising protozoa. It is easy to raise
protozoa in hay infusions. You can make
one by putting dried grass or hay into
water which is then permitted to stand.
Make a hay infusion accordingr to direc-
tions in Exercise io. As the hay decays,
some of its food materials dissolve in the

Fig. 87 This jellyfisb has a long tube tbrorigb
which it eats. With its tentacles it catches and
paralyzes its prey, (aivierican museum of nat-
ural history)

PHYLUM - PORIFERA

Anijnals Riddled with Holes — Sponges

The sponge. Only a few kinds of Por-
ifera (pore-if'er-a) produce commercial
sponges. The commercial sponge is the
tough, fibrous covering or skeleton of
many sponge animals that live in colonies.
The body of a sponge animal, like the
body of the sea anemone and coral ani-
mal, is a simple sac but this sac has many

The Living Things of the Earth unit i

5r?

Fig. 88 Vorticella is one of the vwst interesting
of the protozoa. On the riiii of its open nioiith
is ct row of cilia. Vorticella is anchored by a
stalk. (HUGH spencer)

<>•

Fig. 89 Three aiuebae photographed through a
7/ncroscope. Can you see food vacuoles in the
lowest one? The living material streams in all
directions, (general biological supply)

l"iG. 90 Living Paramecium photographed
through a microscope. The outline is blurred by
the moveme7it of the cilia. Can you see the
groove leading to the mouth? (hugh spencer)

Front end

Contractile vocuole

Macronucleus
Mouth

Cilia

Fig. 91 This drawing of a Paramecium shows
the groove through which food enters. How
does the food get to this spot? What does a
parcrmecium eat? How does it move?

PROBLEM I. The Kinds of AiinuaU

water which takes on a brown tint. Many
kinds of microscopic creatures will soon
be swarming in the infusion.

When pond \\ater is lacking, there-
fore, you may turn to the hay infusion
for your first look at the world of micro-
scopic living things. If you are able to
get the use of a microscope you can look
forward to many happy hours of dis-
covery.

A giant among microscopic animals.
One of the commonest inhabitants of
the hay infusion is an enormous niicro-
organisj/1 (microscopic organism), which
is just visible to the naked eye as a white
speck darting about in the water. You
may have heard its name, Farmjiechmi
(par-a-mee'see-um). Paramecium is easy
to raise and with a microscope fun to
study. Do Exercise i i .

It is not easy to examine a lively para-
mecium with the microscope; it moves
too fast. But it is possible to catch it in
the fibers of cotton or even to thicken
the water so that the paramecium pushes
its way through with difficulty. Either
one of these tricks will slow the animal
enough for you to see that the little sub-
marine-shaped Paramecium is covered
with tiny hairlike parts or cilia (siPee-a).
The singular is ciliinn. These cilia beat
vigorously and thus push the paramecium
rapidly through the water. By lashing
the cilia hard in the opposite direction
the animal can go into reverse. The cilia
are arranged diagonally in rows so that
as they beat they make the paramecium
roll over and over like a barrel at the
same time that it moves forward or back-
ward.

As the paramecium rolls over, one can
see that on one side there is a groove as

oj the Earth 63

though part of its cigar-shaped body had
been scooped out. This depression leads
to a spot, the ynonth. Longer cilia line
the depression; their beat is inward so
that any smaller microorganism caught
by the current is swept to the mouth and
into the paramecium.

The microorganism of ever-changing
shape. Exercise 12 gives you directions
for studying this animal: Aineba. Because
of its habit of clinging to some solid
base and because it is almost transparent,
it is difficult to find. Ameba is not trim
and compact like paramecium, but
spreading and shapeless. Its body is soft
and jellylike — just a blob of living mat-
ter. Some of the living material flows
for a while in one direction and forms
a projection called a false foot or pseu-
dopod (siu'doe-pod). It is a temporary
foot which can form on any part of the
body; in fact, ordinarily an ameba has
several pseudopods at the same time
sticking out in difi"erent directions. Some-
times, however, the material keeps on
oozing in one direction; in this way the
ameba, by ever changing its shape, crawls
along over the surface of some leaf or
stem under water.

The pseudopods are used for feeding
too. If some smaller microorganism or
other particle of food lies in the ameba's
path, false feet flow out above, below,
and on all sides of it and join together on
the other side. The food particle is then
inside the ameba, or, more correctly, the
food particle is inside a little drop of
water which is inside the ameba; for
when the pseudopods join together they
enclose a little water too. If the animal
picks up some w^orthless particle like a
orain of sand, it simply drops it behind as

The Living Things of the Earth unit i

Flagellum

Eye-spot

Green bodies

Fig. 92 Eiiglena is another of the protozoa. It
lashes itself along with the whip-like hair. Be-
cause it covtaijis green bodies soiiie biologists
call it a plant.

it flows along. At one moment the sand
is inside the animal, the next moment it
is out.

There is a giant ameba that your
teacher may be able to show you. It is
called Chaos chaos. It is so large that it
can be detected with the naked eye.

Protozoa swarm in the ocean. One kind
of protozoan which floats near the sur-
face of the sea builds a complicated shell
of lime about its tiny body. Now and
again, when there is a sudden change in
temperature or in other conditions, these
organisms are killed. The millions of
shells fall gently to the ocean floor like
raindrops in a gentle rain. And so many
have fallen throughout the centuries that
deep beds of lime shells have been
formed. Deposits of these shells can be
found at the bottom of the ocean in many
places. The chalk cliff's of southern Eng-
land and the shores of northern France

Fig. 93 Skeleton of a Radiolaria?i. These and
other protozoan skeletons make up much of the
material on the ocean bottom. (American mu-
seum OF NATURAL HISTORY)

are made of limestone rock composed
principally of such shells.

LonCT QCTo seamen noted that there were
nights when the ocean sparkled with a
thousand lights which seemed to dance
on the waves as the vessels plowed along
mile after mile. The light is produced by
enormous numbers of protozoa called
Noctihica (nok-ti-loo'ka). The name
means night light. As many as three mil-
lion individuals may be found in a quart
of sea water when conditions are just
right for their growth. See Figures 92 and
9:5 for illustrations of other protozoans.

The animals in review. Many pages
back you started a studx' in order to be-
come acquainted with the many living
things of this earth. In doing this your
circle of acquaintances among organisms
grew so rapidly that you would have been
hopelessly confused had you not learned
some system for keeping them in separate

PROBLEM I. The Kijids of An'mials

groups. This system is called classifica-
tion. You first studied the mammals, the
animals A\'hich are most closely related
to you, yourself. Then you spent some
time with the birds, the reptiles, the am-
phibians, and the fish. The fish were the
last vertebrates you studied. All of these
had a backbone just as you have. You
then met the invertebrates, the animals
without backbones. It took a long time to
get acquainted with man's insect friends
and enemies and the other, less familiar,
arthropods. From then on you saw mostly
water forms: the shelled mollusks, the
spiny echinoderms; the worms, some of
which burrow in the moist earth; the
coelenterates whose beautiful colors and
unusual shapes remind one of flowers;
and the sponges.

of the Earth 65

There were still many animals for you
to see, but in order to see them it was
necessary for you to equip yourself with
a microscope. Then suddenly a whole
new world opened itself out to you: the
world of Protozoa. A glimpse at these
and you finished your study of the ani-
mal kingdom.

You saw only very few of the almost
one million difl^erent kinds of animals. If
you were to examine each living species
for only one minute and if you were to
keep at it day and night, it w^ould take
you almost two years to review the ani-
mal kingdom. Study of the summary be-
low will give you a scientific view of the
journey you have just completed.

Our attention must now be turned to
the plant kingdom.

Summary

This simpHfied table will help you review the animal kingdom.

Phylum I. Chordates (Chordata): The name is from the word "cord" and refers
not to the spinal cord but to the notochord which is present in adults of some
subphyla and which develops into the backbone of the vertebrates. Most zoolo-
gists recognize four small subphyla other than the vertebrates we have studied.

SuBPHYLUM. Vertebrates (Vertebrata)

Class i. Mammals (Ma?mnalia) : Hair covering. Feed young on milk from

mammary glands.
Class 2. Birds (Aves) : Feathers.

Class 3. Reptiles (Reptilia): Dry scaly skin. Breathe by means of lungs.
Class 4. Amphibians (Amphibia) : Thin, moist skin. All spend first part of

life in water; most later hve on land.
Class 5. Fish (Pisces) : Scaly skins that are moist. Breathe by means of gills.

The sharks discussed on page 32 along with certain other animals make
up another small class. All the other phyla are invertebrate phyla. We
studied the following:

Phylum II. Arthropods (Arthropoda) : A hard outside covering. Segmented bodies

and jointed legs.

Class i. Insects (Insecta): Head, thorax, and abdomen with three pairs of
legs on thorax. Complete or incomplete metamorphosis in their develop-
ment. May live on land or in water. Grasshopper and butterfly.

66 The Living Things of the Earth unit i

Class 2. Spiders (Araclmoidea): Two body parts and four pairs of legs.
Spider and scorpion.

Class 3. Centipedes (Chilopoda): Segmented body. Each segment has one
pair of legs.

Class 4. Millipedes (Diplopoda): Segmented body. Each segment has two
pairs of legs.

Class 5. Crustaceans (Crustacea) : Five or more pairs of legs. Two pairs of
antennae. Live in salt water, fresh water or in damp earth. Lobster, crab,
barnacle.
Phylum III. Alollusks (Molhisca) : Soft-bodied invertebrates with a shell. In some

the shell is internal and reduced in size. Live in fresh or salt water or on land.

Snail, slug, clam, octopus.
Phylum IV. Echinoderms (Echinoderviata) : Radial symmetry, usually with five

divisions. A spiny skin. Live only in salt water. Starfish, sea urchin, brittle star.
Phylum V. Segmented AVorms (Annelida) : Long cylindrical body with segments

or rings. Thin moist skin; most without legs. Earthworm, clam worm, leech.
?Hvi u,M \T Roundworms iN einatbclmmtbes) : Cylindrical body without seirments.

Alany very small, causing disease and living within other animals. Hookworm,

trichina worm.
Phy'lum VII. Flatworms (Platyhehuinthes) : Many live within bodies of other

animals, causing disease. Planaria, tapeworm, liver fluke.
Phylum VIII. Coelenterates (Coelenterata) : Baglike with one opening. Tentacles

and stinging cells. Some free-swimming, some attached, some forming colonies.

Jellyfish, sea anemone, coral. Hydra.
Phylum IX. Sponge Animals (Porifera) : Baglike with many small openings through

the sides. Attached. Some form colonies. Mostly salt water forms. Sponges.
Phylum X. Protozoans (Protozoa): Single-celled. Live in fresh or salt water or

where it is moist. Some live within bodies of other animals and may cause

disease. Some form shells and build up limestone rock.

Questions

1. How do the numbers of yertebrate and invertebrate species compare?
Cite an example of each of the nine phyla of invertebrates mentioned.

2. What name is given to the most complex invertebrates? Give the two
characteristics in which they differ from all other animals. Into Y\hat
five groups (classes) do most of them fit?

3. Describe the principal characteristics of the insects. Be sure to use
the correct terms. Describe the sense organs of a typical insect. How
do some insects make noises?

4. Describe the life story of a buttcrflv, an insect that has complete
metamorphosis. How is incomplete metamorphosis different?

5. Describe the insects with scaly wings. By what three characteristics
can you distinguish moths from butterflies? Name a moth of com-
mercial importance.

6. Which common insects belong to the group of two-winged insects?
What name is given to the larval stage of the fly?

7. Ijst tour relatives of the grasshopper. Describe body regions and ap-
pendages of the grasshopper. Discuss the importance of the grass-
hopper to man.

PRoni.KM I. The Ki/ids of Anhfiah of the Earth 67

8. Cite several examples (jf true bugs. Of what importance to man are
plant lice and scale insects?

9. How can you recognize beetles? List some well known examples.

10. List four common kinds of social insects. Why are they called social
insects? Describe the life history and the community life of ants.

11. How do bumblebees differ from honeybees? Name and describe the
different kinds of bees in a hive. Describe the life of the worker bees.
Describe swarming.

12. Of what importance are termites?

13. State three respects in which spiders differ in structure from insects.
From what is the spider's web built? How is it used?

14. What can you say of the danger of being bitten by spiders?

15. Describe four close relatives of the spider.

16. How do the thousand-leggers resemble worms? Why are they classed
as arthropods? Distinguish between centipedes and millipedes.

17. Name several crustaceans. Where do most crustaceans live?

18. What are some of the peculiar characteristics of lobsters, of crabs, and
of barnacles?

19. Mollusks are divided into three groups. Name one example of each.
What have these three in common? How do they differ? Describe
the shells of mollusks.

20. Describe a snail with a shell. What is a slug?

21. State how the mollusks are useful to man. How are they harmful?

22. Cite an example of an animal that has bilateral symmetry and one that
has radial symmetry. Explain these terms. What are the striking
characteristics of the invertebrates with spiny skins? Name some
examples of this group.

23. Describe the starfish. Include: their appearance, where they live, how
they move about, what they feed on, and how they eat. Define regen-
eration.

24. What are three large groups of worms? What do earthworms eat and
how are they of importance to us? Why are earthworms said to be
segmented? How are leeches of interest to us?

25. In what two respects do roundworms differ from earthworms? What
roundworm causes a disease?

26. What two kinds of flatworms live in other animals? Describe one
kind.

27. Describe the appearance and structure of a sea anemone.

28. Which relatives of the sea anemone live in a limestone shell? Explain
how coral reefs are formed.

29. The jellyfish is a third type of animal whose body is a simple sac.
How does it differ in its habits from sea anemones and coral animals?
Explain how it carries on locomotion.

30. Sum up the characteristics of the animals in this group of coelen-
terates.

68 The Living Things of the Earth unit

31. What are the striking characteristics of sponges?

32. What name is given to the simplest animals? How do they differ from
all other animals? Mention the various places where protozoa may
live.

33. Give directions for making a hay infusion. What use can you make
of it?

34. Define the word microorganism. Explain how the paramecium moves
about and eats.

35. Describe the ameba and its habits.

36. Of what importance are the shell-building protozoa?

37. Imagine yourself starting on a long journey to review the animal
kingdom, passing your own group — the mammals — first and ending
with the simplest forms. Name in order the various groups you would
see.

Exercises

I. If possible obtain a large lubber grasshopper for study. Compare
the three body regions as to size. To which region are the legs and wings
(appendages) attached? How many rings or segments in the abdomen?
Of how m.any pieces is each segment composed? With a hand lens find
breathing pores or spiracles. They are connected with tubes branching
through the body (tracheae). How might overlapping segments help
the insect take in air? Describe the position of the compound eyes. Of
what advantage is this? Look for simple eyes. Describe. What is the ad-
vantage of having antennae segmented? Find a smooth oval spot, the

Fig. 94 Month parts of
the grasshopper. The
two strong, jagged jaws
(A) viove fro?/! side to
side. They are covered
by the lips (B). The
jointed structures like
short feelers hold and
direct the food. These
mouth parts are well
protected by being
tough and horny.
(adapted from turtox
drawing)

PROBLEM I . The Kinds of Avimals of the Earth 60

eardrum, on each side under the wings on the first segment of the abdo-
men. Describe the two pairs of wings and discuss their use. Does your
specimen differ from the picture in the text? How? How many joints
are there in each of the three legs? What is each pair fitted for? Describe
the foot closely. Study the mouth parts and compare with Fig. 94. How
is each part used?

2. How does a butterfly resemble and differ from a grasshopper?
Study a specimen. Follow the directions for study of the grasshopper,
and describe each part of the butterfly. Feel the wing. If you have a
microscope examine some of the powder which comes off on your finger.

3. Since there are half a million species of insects, it would be difficult
to learn much about this large group in a short time. But you will have
made a good beginning if you know exactly how you can recognize an
insect, that is, if you have become acquainted with grasshoppers and
their relatives, moths and butterflies, flies, bugs, beetles, and the social
insects and can distinguish one order from another. Remember that be-
coming acquainted includes recognizing them in all stages of their life
histories. Write up all this in your notebook.

4. Draw a diagram of the top view of an insect and another of a spider
to show the important differences between the two groups of animals.

5. Shrimp and lobsters are easy to obtain in the market; crayfish are
common in fresh water streams. Study and describe the body regions
and the appendages of one of these crustaceans. Study the antennae and
the eyes and compare them with the antennae and eyes of the grasshopper.
What differences can you find among the many pairs of legs of the
crustacean? How might it use these various kinds of legs? What is the
advantage of jointed legs? Of segmentation in the antennae?

If you have live animals, place them in deep water in a large tank and
then in a shallow tray to watch the methods of locomotion. Hold the
crayfish in your hand; does it exert much strength in trying to escape?
Do you think the animal is well protected by its color? Gently touch the
eyes with a pencil. What happens? Have you made any other observa-
tions of your own? If so, discuss them with the class.

6. Arthropods affect man in many ways. Prepare lists of those that
are useful and those that are harmful, telling how in each case.

7. You have become acquainted with four groups of arthropods be-
sides the insects. Name a few forms in each of the five groups. Tell how
they live.

8. Dissection of a clam. If you crack one valve of the shell and remove
the pieces gently you will see the mantle, a thin skin next to the shell,
and the gills. Can you find the muscles that hold the shells together?
Open an oyster and compare its structure with that of the clam.

9. Collect some earthworms and keep them in a box of earth with glass
sides. Watch them. Write up your observations briefly but accurately.

10. To study the organisms in a hay infusion. Boil a small handful of
hay and two or three wheat seeds in half a quart of water. Allow it to

-JO The Living Things of the Earth unit i

stand for several days; then add a little pond water. In about ten days you
should have a good hav infusion. To slo\\' up the protozoa for study vou
can add to your slide a little gum tragacanth (ask for it at the drug store).
You ^\•ill find instructions for the use of the microscope on pages 1 13-1 14,
How many kinds of protozoa do you see? Draw some.

11. How does a paramecium move? Which seems to be its front end?
As it swims forward it rolls over. Does it roll clockwise or counterclock-
wise? Which way does it roll \\'hen it swims backward?

12. Perhaps the most fascinating object to watch under the microscope
is a large ameba. Do not use a bright light. How many pseudopods do
\ou see? What seems to happen to the particles just inside the tip of a
pscudopod at the "front" end of the animal? Does it ever lose a pseudo-
pod? How do you know? How fast does it move? How does it change
direction? Does it ever reverse the direction of its movement?

Further Activities in Biology

1. How to raise and observe grasshoppers. Construct a cage. Cover the
bottom of a terrarium with sod on which grass is still growing. The grass
must be watered regularly for the grasshoppers eat the grass and are
dependent on the water which they get from the surface of the leaves.
Cover the cage with a wire top or with a mosquito netting. Watch the
insects eat. Observe all other activities.

2. How does the grasshopper jump? If you can obtain live grasshoppers,
watch' them jump. How many times its own length does a grasshopper
jump? In what position are the hind legs when the insect is about to
jump? Compare a grasshopper with a man doing a broad jump. Explain.
Does the grasshopper use its legs for anything but jumping?

3. If you have any plants in the house or garden, examine the stems
and leaves carefully for aphids or scale insects. Describe any that you
find. Some kinds can be removed by holding the leaves and stems in soapy
water.

4. Perhaps your class or biology club could buy an observation beehive
to keep at the window of your laboratory. You will learn a great deal
about the life of bees.

5. Alany books have been wTitten on the social insects. Prepare a full
report on one of the social insects.

6. Daphnia is a tiny crustacean that is easy to obtain and raise. Write
to an\' large biological supply house and ask for directions.

7. rhe development of the snail is easy to follow if you use a hand
lens. Keep several snails in an aquarium. The eggs are laid in masses, often
on the glass. Note whether all the offspring of snails with right-handed
shells also have right-handed shells.

8. Shell collecting is so popular a hobby that there are dealers all over
the world who publish catalogues of both common and rare kinds.
Encyclopedias contain pictures in color of some of the most beautiful.

PROBLEM I. The Kinds of Ajii7nals of the Earth 71

Make a collection of your own, using a shell book to learn the names
of the animals. By exchanging specimens you may he able to get shells
from other parts of the country.

9. The complete story of Charles Darwin's study of the effect of the
earthworm on the soil is told in his book, The Fonnatioii of Vegetable
Mold. It is not difficult to read. Prepare a report for the class.

10. If you follow directions carefully you can maintain a salt water
aquarium. Starfish, sea anemones, and mussels will live in it if you have
plenty of seaweed. A Turtox leaflet (General Biological Supply House,
Chicago, Illinois) will provide complete directions. You may buy the
plants, animals, and sea water from biological supply houses if you are
far from the coast.

1 1. If you are talented in drawing prepare a mural for the walls of your
classroom, showing examples of animals in each of the phyla from the
sponges to the arthropods.

12. If you have a good hay infusion and are skillful with the micro-
scope, make daily observations and keep accurate notes. Always take
samples of water from different levels in the jar. You will make an inter-
esting discovery in the course of several weeks.

13. Have you ever thought of owning a microscopic pet? It is really
easy. Paramecia make the best pets because they are hardy. By heating
a piece of glass tubing soften it until it can be drawn out to make a very
narrow tube. Break this narrow tube so that you have a pipette with a
narrow opening. Put a slide containing paramecia on a piece of black
paper so that the paramecia can be seen with the naked eye. They will
appear as white specks. Catch one by dipping the pipette into the water
near it. Draw the pipette out quickly so that you catch only one para-
mecium. Gently blow the paramecium out on another slide. Add some
cool boiled hay infusion water. Then put the slide in a Petri dish (ask
your teacher). The Petri dish must contain a piece of blotting paper
soaked in water. This will moisten the air. To keep the bottom of your
slide dry, put it on two match sticks that lie on the blotting paper. Cover
the dish. The next day you should have two or more paramecia. Repeat
this process, discarding one of the animals, and keeping the other.

PROBLEM / What Kinds of Plants Inhabit the Earth?

The two large groups of plants. In de-
scribing animals it was convenient to
speak of animals with a backbone and
animals without a backbone. Later we
sorted those without a backbone into
different phyla. In describing plants we
again very simply speak of two kinds,
those with flowers and seeds and those
without. People sometimes carelessly use
the words flower and plant as though
they mean the same thing. The flower, or
blossom, is only part of a plant, just as
the eye or the heart is only part of an
animal. Some plants bear flowers at cer-
tain times in the life of the plant. Others
never bear flowers. The plants that never
bear flowers are not the trees and the

grasses which you may be thinking of.
Trees and grasses have flowers although
they are often so tiny or so unlike ordi-
nary flowers that they may escape your
notice. Trees and grasses are therefore
flowering plants, together with roses and
violets and daisies and many others.

The true "plants without flowers" bear
no flowers of any kind nor do they form
seeds; and besides, as you will see, most
of them differ from the flowering plants
in their general make-up. Some differ so
widely that you might not recognize
them as plants at all. You will study the
plants without flowers first. There are
three divisions or phyla of flowerless
plants.

THALLOPHYTES

Agaricus

BRYOPHYTES

Pigeon-wheat moss

Fic. 95 Examples of the four large groups in the plant kingdom. Which of these groups

PROBLEM 2. The Kinds of Plants of the Earth

Flowerless Plants

PHYLUM - THALLOPHYTES

The simplest plants. The first division,
or phylum, of the plant kingdom con-
tains plants which differ widely among
themselves in appearance and in size.
Som.e are single celled and microscopic;
others grow to an enormous size. All
are alike in that they do not have true
roots or stems or leaves and that they
never produce flowers or seeds. Some
contain the green coloring matter so
characteristic of plants. They are called
Algae (aPjee). Those that lack the green
coloring matter are called Fungi (fun'-
jeye). Of the algae some look bright
green; in other algae the green coloring
matter is more or less hidden by other
colors so that these algae may look bluish
green or even brown or red.

The smaller algae. Have you ever seen
a green scum on the water of a slowly

moving stream or small pond? If you
lift the scum on a stick you discover that
it is a bright green mass of long tangled
threads. Each thread consists of a number
of cells all alike. If you examine these
threads with a microscope, it is likely
that you will see a beautiful plant called
Spirogyra. Each cell contains one or
more green spirals. The plant has neither
root nor stem nor leaf. See Fig. 97. It
is just a living green thread which grows
in the sunny water and may at some
time become food for a water animal.
With a microscope you can do Exer-
cise I.

In the plant kingdom as in the animal
kingdom, the simplest organisms are
usually water dwellers. Some of these
simple plants have one or several long
whiplike projections by means of which
they swim. Yes, many species of simple
plants move about. Others, such as the

PTERIDOPHYTES

Christmas fern

Naked seeds

SPERMATOPHYTES
Covered seedst*

Pine tree with cones

ooming geranium

are flowerless plants? How many other examples of plants hi each gronp do yoii know?

The Liv'wg Things of the Earth unit i

Fig. 96 Life hi salt ivatcr. This is a coiiiDioii si^bt for those ivho live near rucky ocean
shores. Do you see the strands of rockiveed? To what large group of plants does it
belong? What animals do you recognize? (American museum ok natural hisior's )

ri^^T"^

v.<»

•« v*> v

■,// i ;• \ ^ * ^' ^'^

•*:>'«

^^^.^

Fig. 97 P^i of a single strand of Spirogyra, one of the pond scums. Do you see lUe
spirals? They are bright green. Spirogyra lives in fresh water, (general biological
supply)

diatoms, have l)cautifull\- ni;ir1v'cil sliclls.
They hve in enormous numl)crs in salt
and fresh w arcr, serving as food for ani-
mals. The shells of those that lixxd mil-
lions of years ago have accumulated and
are (juanied ami used in manv ways.

.•\ few of the simple plants live on land,
usualh' w here there is plent\- of moisture,
although some of them can stand much
dr\-ing up. ihe \er\- rhin (Tat (rrecn

growth found on the bark of trees is a
mass of simple plants called Vrotococais.
You may have called it moss, but its
structure is very different from that of a
moss. Closelv related to it arc the altjae
which grow by the millions on the snow
during the summer in arctic regions.
I'A'plorers call these algae "red snow."

Larger algae. There arc other larger
ahj^ae, that (jrow in salt water, the sea-

PROBLEM 2. T]?c Kliids of Flavts of the Earth

Fig. 98 Tiyis Amanita is very poisonous. It looks Fig. 99 The bracket fungus is related to the
much like the coimnon imishroom which you nmshrooins. Most of the plant is under the bark,
can buy in a market, (blakiston) (u. s. forest service)

\\eeds. Some, like the common brown
seaweed or rockweed {Fiiciis — few'cus),
are fastened to the rocks in the region be-
tween the tides. They can hold much
moisture and are tough enough to stand
the pounding of the surf. Some brown
seaweeds, like the kelps, may reach a
length of fifty yards or even twice that
length. Formerly kelps were burned to
yield iodine. They \\ere gathered in large
amounts off the coasts of Ireland, France,
and elsewhere.

Other seaweeds float near the surface
in the open sea. You may have seen pieces
of the green sea lettuce (Ulva) which
have been washed ashore and caught on
the sand or rocks. At greater depths
live red seaweeds, which are usually deli-
cately branched plants of much smaller
size. The agar-agar which the drug store
sells and which is used in some experi-
ments comes from a red seaweed found
near Japan and near our west coast.

Mushrooms. As you read above, the
simplest plants without flowers are of
two kinds; those with green coloring
matter, the algae; and those without
green coloring matter, the fungi. Among
the larger more conspicuous fungi are
the mushrooms. About one half of the
many kinds of mushrooms make good
food. Some are too tough to be eaten and
some are definitely poisonous. It is often
so hard to tell the various kinds of mush-
rooms apart that no one but an expert
should decide which can be eaten. Mush-
rooms live only where it is damp. Most
are small, but some attain a weight of
more than thirty pounds. Study a com-
mon mushroom. See Exercise 2.

Fungi you do not like — the molds. In
damp weather stale bread often begins
to smell musty — the peculiar smell of a
fungus know^n as jjwld. If you give the
mold a chance to develop and then ex-
amine it closely you will see that what

The Living Things of the Earth unit i

Fk;. ioo l)rawmfi,s of several kinds of fresh-water algae. Hundreds of kinds of algae
are found on soil and in sivan/ps, lakes, ditches, and streams. Algae are the principal food
of many kinds of small water animals, and these animals are the food of larger animals.
The names of the algae are: (A) Stigeoclonium, (B) Chaetophora, (C, D) Oedogo-
vimn, (E) Anahaena, (F) Micrasterias, (G) Euastrum, (H) Staiirastruni, (I) Penimn,
(J) Scytonema, (K) Amphiplc/ira, (].) Stictodiscns, (AI) Suriella. (redrawn by per-
mission KROM Textbook of Botany, iranskau, sa.mpson, and tiikany, harper and

HROTIIERS)

PROBLEM 2. The Kinds of Plains of

at first looks like an ugly mass is really
a very delicate simple plant. In fact, the
bread may serve as a garden for several
species of beautiful mold plants. The
commonest one, known as the bread
mold or Rhizopus (ry'zo-pus), consists
of a miniature jungle of very fine, glis-
tening, white threads. Little black balls
appear at the tips of upright threads.
These make the mass of white threads
look gray and later sooty.

You can raise a variety of molds by
doing Exercise 3. Molds grow on many
different foods if enough moisture is
provided. There are some mold plants
that look like patches of bright blue-
green felt; others are salmon pink. The
drug penicillin is prepared from some of
the blue-green molds. In these the threads
are shorter and even more interlaced so
that without a powerful lens you cannot
see separate threads at all.

A plant that is both alga and fungus
in one. Strictly speaking, this "plant" is
two separate plants, one an alga, the
other a fungus, but they are so closely
combined that they look like one plant.
The combination is called a licheii (ly'-
ken) . It looks grayish or yellowish green.
You may have seen lichens on rocks or
trunks of trees. Some, like the "reindeer
moss," grow on the ground.

Lichens are extremely hardy plants;
when all else has been killed by the cold
they still survive. They are food for
grazing animals, such as reindeer, of the
arctic zone. Some are eaten by man.

Fungi that help man bake and brew.
The yeast plant is so small and so simple
that even under the microscope it does
not look like much of anything. It is
merely a tiny, colorless, tg^ or rod-

the Earth

shaped speck which cannot move. See
Figure 362, page 413. It is classified as
a plant and is clearly a fungus.

There is one special kind of yeast that
we raise in vast numbers. Millions upon
millions of them are pressed into one
yeast cake. Yeasts are useful because
when they live in sugar solutions they
change the sugar into alcohol and a gas
called carbon dioxide. This change is
called fermejjtation. When we want to
bring about fermentation we often put
yeast plants with soaked, crushed corn
or other grains. When we make wines
we add yeast plants to grapes, although
until recently we depended on "wild"
yeasts to change the sweet fruit juice into
alcohol. Wild yeasts and molds, too, float
about in the air. You are now ready for
Exercises 4 and 5.

Yeasts, as you may know, are also used
in baking. They cause fermentation in
the dough but the alcohol evaporates
during the baking so you never taste it;
the carbon dioxide gas forms bubbles in
the solid mass of dough, "raising" it and
making it light and porous.

Bacteria. These very important plants
are usually classed as fungi, although
some biologists place them in a phyluni
by themselves. Most bacteria are so much
smaller than yeasts that they are difficult
to describe. As a matter of fact, there is
probably not much to be seen in them.
Most of them cannot move about but
some can wriggle when in a liquid and
a few can swim by means of long whip-
like projections. There are giants and
pygmies among bacteria, but even the
few giants are so extremely small that
they can be seen only with a good micro-
scope. It has been calculated that if the

The Living Things of the Earth unit i

Fig. loi Bacteria that cause pueinnonia. The
photograph was taken through a microscope.

(AiMERlCAN MUSEUM OF NATURAL HISTORY)

bacterium which causes one kind of
pneumonia \\ ere magnified to the size of
a tennis ball, and if the man in whom the
bacterium lodges were magnified in pro-
portion, the man would be about twenty-
five miles tall! But bacteria are interesting
to man not for the way they look but
for what they do. Some species live in
man and cause disease but many more
are harmless or even \aluable. You will
read more about them in Unit VI.

PI n LUM - BR^'OPHVTKS

The Mosses and Their Relatives

The second large di\ ision of flowcrlcss
jjlants. This group includes the mosses.
rhc\ look somcw hat more like the plants
commonly recf)gnized as plants. For one
thing, most of them live on land. I'or
another, they are always green ami, like
the plants you know best, are anchored
ro the soil. Then, too, moss plants have
simple le;ncs and rootliK'C and stemlike

Fig. 102 thyscuiiiitriuin, a tiny moss that you,
may find in your garden. It is less than one-half
inch high, (hugh spencer)

parts. Mosses range in size from less than
one-eighth inch to more than one and
one-half feet high.

Mosses gro\\- almost everywhere ex-
cept in salt water. There are vast bogs
of one kind of moss known as Sphagmnn.
The sphagnums are among the largest
of mosses, having^ a stemlike part that
grows to be many inches long. Stems and
leaves are constructed so that they absorb
water like a sponge and for this reason
some kinds were formerly used for dress-
iniT wounds. The greatest usefulness of
sphagnums arises from the fact that
w hen they gro\\- in w arcr, the plants do
not decay when they die. The accumu-
lated dead plants become w hat is known
as peat. Peat accumulations many feet
deep are common. After draining the
bog, the peat can be dug out in small
squares, dried and used as a fuel.

PROBLEM 2. The Kinds of Vlants of the Earth

Fig. 103 The bay-scented fern. Not all jerns
have leaves {fronds) as finely divided as this.

(SCHNEIDER AND SCHWARTZ)

PHYLUAI - PTERIDOPHYTES

Ferns and Their Relatives

The third large division — the ferns.

There is something about a fern that
pleases the eye; for that reason you have
all noticed ferns. They have been culti-
vated, too, so that they are often seen
in homes. There are almost four thou-
sand different species growing in many
parts of the world. Most species need
moisture and thrive best in the shade of
forest trees. But some, like the sensitive
fern, live on the edge of the forest; a few,
like the bracken or brake, grow in sunny
fields. Alost fern leaves (called frojids)
are divided and often finely subdivided
into leaflets. The leaf comes up from
the ground tightly coiled like a flddle-

FiG. 104 The ^^scouring nisb" is a relative of the
fern. It is harsh and gritty to the touch. (Brook-
lyn BOTANIC garden)

head; as it grows, it uncoils and spreads
out its broad surface. In most ferns the
leaves are the only parts that are visible;
the woody stem lies underground and
may extend for many feet just under-
neath the surface of the soil. Like all
the plants you have read about so far
ferns never form flowers or seeds.

In the tropics ferns grow to a much
greater size and some develop strong
stems above ground. In fact they may
grow as trees sixty or more feet high.
And there was a time some 200 million
years ago or more when large tree ferns
grew in vast numbers much farther north.

The

Large portions of the rich coal deposits
of Pennsylvania are the remains of these
ancient fernlike plants. And in those past
ages, two small inconspicuous relatives
of the fern also grew as tall trees, the
chib moszes and the horsetails.

The club mosses are also commonly
called ground pines. Thev are creeping
plants that grow close to the forest floor.
It is difficult to say which name is least
fitting since they are neither "mosses"

Living Things of the Earth unit i

nor "pines." They are closely related to
the ferns. Another common name for
the horsetails is scouring rush (Figure
104). All the species included in this
division or phylum have true roots, stems,
and leaves, but they never bear flowers
and they never produce seeds.

If specimens are available, you should
now be able to do Exercise 6. The whole
class might \\ ell make a common project
of Exercise 7.

Plants with Flowers and Seeds

PHYLUM - SPERiMATOPHYTES

Characteristics of flowering plants. The

plants of this, the fourth large division,
not only produce flowers and seeds but
they have another characteristic which
is not possessed by any of the simpler
plants except the ferns: they have well-
developed roots, stems, and leaves. There
is great variety in the size and appearance
of these parts, as well as in the blossoms,
as you can imagine when you learn that
there are more than 125,000 different
species in this division. They are the
commonest land-living plants. But some
grow in water. In fact they may be found
in almost any environment. Some have a
stem that is soft, grows rapidly, and dies
at the end of the year. They remain small
and are called herbs. Others have stems
that are woody and tough. If the\' have
one main stem, they are trees; if they
h;nc several equall\- thick stems arising
from the ground, in which case they
iisualK do not grow very tall, they are
called shrubs.

Flowering plants vary, too, in kngili

of life. Those that start from seeds, grow,
produce flowers and seeds and then die
during one growing season are called
ammals. Examples are the crabgrass, com-
mon as a weed in many lawns; radishes,
tomatoes, and lettuce of the garden, and
farm crops such as oats, corn, and buck-
wheat. Plants that start from seeds during
one growing season but produce flowers
and seeds and then die during the next
season are called biennials. Many weeds
are biennials. Among the farm and gar-
den crops that are biennials are winter
wheat, cabbage, and carrots. You M'ill
note that both annuals and biennials die
after flowering. The other seed-pro-
ducing plants are called peremiials. These
plants may live for many years, produc-
ing flowers and seeds each growing sea-
son. All of our trees and shrubs are
perennials as arc certain garden and farm
crops such as asparagus, sugar cane, and
tulips. Perennial grasses make the finest
lawns. Perennial plants may live to a great
age. The cypress of Mexico and some of
the big trees (sequoias) of California
ha\e lived for 3000 to 4000 years.

PROBLEM 2. The Kinds of Vlams of the Earth

Fig. 105 All the plimts yoii see m this photograph are Sperinatophytes. They hear
flowers and seeds. If you were to go to the scene of the photograph, where would you
be likely to find algae atjd fungi, mosses and liverworts, and ferns and horsetails?
(eva luoma)

The two chief groups of flowering or
seed plants. This division includes plants
that you may not have thought of as
"flowering" or seed plants, the cone
bearers.

Thus there are tw^o large groups in this
phylum:

1. The cone bearers and their relatives
(Gvrnno sperms — jim'no-sperms).
Botanists think of them as seed
plants with u ncovere d or naked
seeds.

2, The true flowering plants (Angio-
sperms — an^iee-o-sperms). To bot-
anists thev are the seed plants wdth

covered seeds.

The cone bearers. The scales of the
cone hold the uncovered or naked seeds.
These plants are called conifers (kon'i-
furs) and most of them are evergreen.
The leaves of conifers are usually hard
needles or tiny scalelike leaves which can
withstand the winter drought (lack of
moisture) and cold. The needles live for
two or more years, so the trees remain
green at all times. There are many dif-
ferent kinds of conifers or evergreens:
the giant redwoods of the west, the many
kinds of pines, firs, hemlocks, cedars, and
smaller plants or shrubs like the yews.
Some people carelessly call many of the
evergreens "pines." The true pines are

The TJv'wq; Thh]Q:,s of the Earth unit i

easily recogni/cd because they have
longer needles than any other cone
bearers, and their needles grow in
clusters.

In the temperate /ones the conifers are
of great \ahie for their wood which is
known as softwood. Most of thcni have
a very stickN' sap which has a strong,
peculiar odor; it is called resin. The wood
i)unis up too fast to l)e gooil firewood,
but most of our lumber is sawed from

\'h.. iu6 (above left) Red cedar. Its cone is
hidden within a so-called berry. (American mu-
seum OF NATURAL HISTORY)

Fig. 107 (above) Pine. (Brooklyn botanic

(IAROEN)

Fic. loS (left) Hemlock. Hove does it differ
fro//; pii/c ai/d red cedar? (dickerson)

the trunks of conifers. They are of great
importance, too, as a source of wood for
making paper.

The true flowering plants. The true
flowering plants are far more numerous
and more varied than the cone bearers.
The group includes plants as different
as a small grass plant and an oak tree,
for both bear flowers and produce seeds,
and they resemble each other in various
other ways. However, there are iiupor-

PROBLEM 2. The Kiihis of rimits of the Earth

Fig. 109 (above) Chestmit. These leaves have
feather net veining. (schneider and schwartz)

Fig. 1 10 (upper right) Maple. These leaves have
palviate net veining. (schneider and schwartz)

Fi(,. 1 1 1 (right) This lady's slipper, an orchid,
has the typical parallel-veined leaves of mono-
cots, (gehr)

tant differences, too. G rass plants a re
representatives of one large division of
the flowering plants, the vionocotyledons

(mono-cot-i-lee'dons) or monocots for
short. Oak trees represent the other large
division, the dicotyledons or dicots for
short. It is easy, for TRSti 10s L pal L, Lu Lcll
these two groups apart. Thelea^xs ^of
the__jiionQi iots have ma tiy Inng y.^*^
running from one end of the leaf to the
other and close to one anoth^er. SeeFig-

ure III. The leaves of the dicots have
vems and a laTge net-

few

)rinc

wo rk of smalle r veins. See Figure no
and do Exercise 8. You will learn other
differences between monocots and dicots
but you must not get the impression
that all monocots are small and dicots
large. In both groups there are large and
small plants.

There are so many kinds of flowering
plants that botanists find it convenient

The Livwg Th'mgs of the Earth unit i

to subdivide the monocots and dicots
into families. There are more than two
hundred and forty famihes in the group
of dicots alone and many families among
the monocots. Each family contains, as
a rule, many different kinds or species.

Monocotvledons used as food. The
monocotyledons are the source of much
of your food. This may astonish you, for
many of these plants are small and un-
important looking. But although they
are relatively small they occur in great
numbers; they grow side by side in end-
less stretches of field and meadow and
lawn. They are food for the cattle, sheep,
hogs, goats, and other grazing animals
which are raised for their meat or milk.

We use grasses of various kinds as
food plants for ourselves, too. The "ce-
reals" or grains su ch as w^hea t^^mts,
barley, riceTanid^corn are close_relatiyes
o^rhe'small wild grasses oToiir meadows
and lawns. All of them are monocoty-
ledons as you can see if you examine the
leaves. These cereal plants have been
cultivated for many thousands of years.
The cultivation of these plants has gone
on so successfully that over five billion
bushels of \vheat alone are now produced
in the world each year. When you real-
i/,c that it is only the small kernels or
seeds of the plant that are gathered to
h'll the bushel baskets you can appreciate

I'll;. 112 (top) Tmiothy, a grass plant. Each
spike is a mass of tiny flowers, (blakiston)

Vhi. 1 1\ (bottom) Sugar cane, like timothy, is a
inoiiocot. How tall does it grow? (u. s. bureau

OF PLANT industry)

Fig. 115
Poplar. A
very covi-
ijion tree.

(BROOKLYN-
BOTANIC

garden)

PROBLEM 2. The Kinds of Plants of the Earth

how many acres of wheat there must be.

In the tropics there grow the large

banana plant and a giant grass, the sugar

cane, that makes much~orThy Sllgar eateTT

uonocotyledons, as the

by -man . S t

d^te and coconut palms,^re~trees. Tfiey

supply mucli^food. n

Many dicots are trees. You have already
read about the cTTrTC'''5earers; the rest
of our native trees are dicots except for
one or two palm species which grow in
the semitropical climate of Florida and
southern California. A4ost dicot trees in
our country shed their leaves at the end
of the season and are for this reason
called decidi/07 /s (de-sid'you-us). The
deciduous trees are rather generally re-
ferred to as "hardwoods" by foresters
and lumbermen.

There are several families of trees
widely spread through large portions of
the United States; you are probably
familiar with most of them. If you can
recognize oaks^^ jjiaples . elms, and.hic k-
ories or walnuts you are acquainted with

Fig. 1 16
Oak. This
and the
poplar and
ehii have
feather net
veins.

(AMERICAN
MUSEUM

of natural
history)

Fig. 114 This shagbark hickory leaf is a coin-
pound leaf. (brookly'N botanic garden)

u..

Fig. 117
Elm. H01V
can yon
recognize

it? (AMERI-
CAN MU-
SEUM OF
NATURAL

history)

Fig. 118
Red maple.
How can
yon distin-
guish this
Tiiaple from
the one in
Figure 110?

(AMERICAN
MUSEUM OF
NATURAL

history)

The Living Things of the Earth unit i

I'k;. 1 19 Tl?e i^ild rose. Hoiv does it differ froiii
all the many cultivated roses that you have
seen? (Brooklyn botanic garuen)

at least one member of each of four
prominent tree families.

Another family that many of you will
know includes the \\ illows and the pop-
lars. You often see willows lined up along
the banks of streams. In dry, otherwise
treeless regions, a group of poplars al-
ways is a sign of water trickling through
the soil. Their wood is unusually soft
for hardwood trees and is therefore
much used for paper making.

All these trees bear flowers although
the flowers of many of them are so small
that you might not recognize them as
flowers.

The rose family. There are some fam-
ilies rhar coiiraiii species ranging in size
all the wav from a small, soft-stemmed
herb to a gootlsizctl shrub or tree. They
are grouped together in one family
largcl\ because of their similar flowers.
'I'he rose family, for example, includes,
among man\- other plants, the trees that
bear pears, peaches, plums, or apples;

Fig. 120 Strawberry blossoms. Can you see ivhy
strawberries and roses are placed in the sa7ne
fainily? (hugh spencer)

it includes also the shrubs that produce
raspberries and blackberries, the bushes
which bear roses, and the still smaller
strawberry plant. You may not be able
to obtain a blossom of this family for
study at this time. But you might wish
to study some other flower to learn its
parts. See Exercise 9. In some species of
the rose family the flower is small, in
others it is large and showy, but on close
examination you would see that all the
blossoms are similar and most of them are
rich in nectm\ the sweet liquid that can
be changed into honey by bees. Farmers
sometimes place beehives in apple, plum,
or peach orchards in order to get a
better fruit crop. You will read later
how in obtaining nectar and pollen the
bees help to make good fruit.

The clovers and their relatives. Some
of the plants in this famih' are also
sweet-scentctl; and some form edible
fruits. The clovers have blossoms that
are small, l)ut gathered so closely into a

PROBLEM 2. The Kiuds of Flants of the Earth

P'iG. 121 Each blosso?n in a head of clover is Fig. 122 The potato plant has ^vhite or pale
vot nnlike a pea blossom. To ivhat family does lavender flowers. But the farmer plants pieces
clover belong? (root) oj potato, not seeds, (blakiston)

head that life is made easy for the bee
that dips its sucking tube into the nectar
bags.

In the same family with the clovers
are the sweet peas with their showy
blossoms, as well as the more humdrum,
practical garden peas, and beans. Both
peas and beans produce large fruits,
which are the pods we know as vege-
tables.

Another member of the family is al-
falfa (al-fal'fa), which means in Arabic,
the best fodder. Alfalfa is now grown
throughout our country. The family also
includes the decorative woodv climber.
Wisteria, and among the trees, the vQVf
useful black locust.

Other families that furnish food — the
potato family. Th e, dicot ylgd on^ tha t is
now raised, perhaps more than any other,
to supply man with food is the potato.
You may have read how it was intro-
duced into Europe by the Spaniards and
by Sir Walter Raleigh. In the same family

with the potato are tlie tomato, the pep-
per, the tobacco plant, and the poisonous
nightshades.

The mustard family contains many
members that have been cultivated to
supply us wath "vegetables." The mus-
tard family usually has small blossoms
with four petals arranged in the form of
a cross. Among the plants of the mus-
tard family are some of the strong-tast-
ing vegetables: turnips, cabbages, cauli-
flower, brussels sprouts, and others. Of
course, the onion and the leek do not be-
long here; if you have ever looked at
their leaves, you know that they are
plants with parallel-veined leaves, mono-
cotyledons.

The parsley family is another large,
well-known family. Most of its members
have deeply cut compound leaves, like
the table parsley, and tiny flowers
grouped together in a flat-topped cluster.
You may have seen the lacy wild car-
rot dotting the fields with white after

The Livmg Thifigs of the Earth unit i

Fig. 123 TP/W carrot. Another name is Qiteen
Anne''s lace. This is a nieiiiber of the parsley
family. (uRooKi.-i x hoianic garden)

the daisies are gone. Related to it is the
carrot which is raised as a vegetable, the
many parsnips, both wild and cultivated,
and celerv. Like the potato family, it
also has its "black sheep," the poison
hemlock, which yields a powerful poi-
son. The ancient Greeks used a drink
brewed from it to put Socrates to death.
Of course, the poison hemlock is not at
all closely related to the evergreen tree
named hemlock.

Tlie mint family. You have met some
of the members of the large mint fam-
ily: peppermint, spearmint, pennyroyal
(sometimes used against mosquitoes),
and sage. Some are used to lend flavor to
food, but some species of this family lack
(la\()r (ti- otior. Ihc flowers are for the
most part small. Ihe'stems are four-sided.

Plant families that have proved useful
in various wavs. \\ hen Cohinibus Jainicd

Fig. 124 The white floivers and red berries of
the coffee tree. Each berry contains two coffee
'''' beans.'''' (American can co.)

on the shores of South America he found
the natives playing with a black ball
that apparently moved and seemed alive.
Several centuries later the substance of
which the ball was made came into gen-
eral use in Europe for "rubbing" out ink
and pencil marks. That was the white
man's first introduction to "rubber," as
he soon learned to call it. Rubber is
made from a milky liquid produced by
numerous tropical trees belonging to
many different families. It can be ob-
tained from other plants also.

I'^u" older than the rubber industry is
the raising of cotton plants. The fruits,
when ripe, burst open sho^\•ing a fluffy
mass of white threads, w hich arc attached
to the seeds. See I'igure ^ ^9, page 390.
The cotton gin is used to separate the
seeds from the "cotton." The seeds them-
selves are squeezed to remove their valu-

PROBLEM 2. The Kljuis of Vlaiits of the Earth

Fig. 125 Camoviile is a com-
mon composite. About how
f/hviy ray flowers surroimd
the yellow disc? (Brooklyn

UDTANIC garden)

^..

-^ ,

- JV

'*^jSr

^^^^^^VSfik, t^'B ^^^^^1

^af

-Vr %%,.

f , ,^^'if'^1

^v^!^If

'.-. *"^^

^^^^^n^^

t^S^SJ^Sf^ '•"^ *■ 'flK^vL

iKttoJH

able cottonseed oil, which is used for
making oleomargarine, salad oils, and for
many other purposes. What is left of
them can be ground up to make food
for cattle, can be used in making plastics,
or spread on the ground as fertilizer.

We get threads or fibers in a very dif-
ferent way from the flax plant. It has
beautiful bright blue or white flowers.
Although its leaves look somewhat like
those of a grass, it is a dicotyledon. The
threads which are later woven into linen
come from the stems which must be
"retted" or rotted in water. This loosens
the threads. Its seeds are also used as a
source of oil (linseed oil) and as cattle
feed. Linseed oil is a part of many paints.
There are plants of various families like
hemp and jute whose stems or leaves
contain tough fibers which are used for
making rope or coarse bags.

Another family of importance to man
is the madder family. Among its useful

members is the cofl'ee plant. Originally
at home in Abyssinia, it has been carried
to many parts of the w^orld where the
cHmate is warm. Two other members of
this family are the cinchona (sin-koh'-
na) tree, whose bark yields the drug
quinine, and the madder, which has been
used to dye cloth from the time of the
early Egyptians.

The composites. You have seen daisies
in the pasture and dandelions in the lawn.
What you have probably always called a
daisy blossom is really a tiny bouquet
of many small blossoms. The daisy is a
very closely packed cluster of two very
different kinds of flowers. The yellow
portion in the center consists of a large
number of tiny flowers packed together
so tightly that you need to look closely
before you can distinguish them as sep-
arate flowers. Around them are the much
larger white flowers, called "ray flowers"
from their position around the center

disc. Many plants in this family do not
have the striking ray flowers. But all the
plants in the composite family bear many
small flowers in one head so closely
grouped that the head looks like a single
blossom.

There is almost no end to the species
of composites. Some may grow on rub-
bish heaps and in uncared-for city lots.
Here you will find the burdock, w^hich
children often call "stickers," and the
cocklebur with its vicious burs. Along
the roadside grows the ragweed respon-
sible for hay fever: and where the grround
is damp, the wild lettuce. In the vege-
table garden you will find the artichoke,
oyster plant, lettuce, and chicory. These
are all composites. It is by far the largest
family among flowering plants.

Now the class might sum up the pages
on angiosperms by doing Exercise io.

In the last problem vou examined the
complex animals first and you ended
with the simplest forms. In this problem
you began with the simplest fonns and
ended with the most complex. "\'ou
learned about algae, simple water plants
that never bloom and that have no root
or stem or leaf. You learned about many
simple plants that were not even green and

The Living Things of the Earth unit i

often did not grow in soil. These were the
fungi, the microscopic plants like bac-
teria and yeasts, the many molds, and
the much larger mushrooms. Later you
studied the more complex mosses and
then the larger ferns. You found that the
ferns have leaves and stems and roots
but bear neither blossoms nor seeds nor
fruit.

Finally you studied two large groups
of plants that looked like plants. First
you looked at the evergreens that bear
cones and then at the real flowering
plants. You learned something of mono-
cots, the grasses, orchids, lilies, and palms,
and of the dicots, which are used in so
many ways. There were tall trees and
tiny herbs. At first glance these seemed
to differ much among themselves but all
of them had a root, stem, and leaves; all
bore blossoms or cones, and all produced
seeds.

In this study you met plants you had
not seen before. You were assisted in
learning their names by gathering them
into groups or classifying them. In the
next problem you will read how, many
years ago, a scheme was devised for
naming and classifying the many living
things of this earth.

Summary

This simplified tabic will help you review the plant kingdom.

PHYLUM 1. Thallophytes (Thallophyta): Plants without flowers and fruit. Also
lacking root, stem, and leaf.
SUBPF^'S'I.UM I. Algae: Simple thallophytes with green coloring matter. With

few exceptions, acjuatic. Green, hrown, and red seaweeds and other plants.
SUBPin'LUAl II. I'ungi: Simple thallophytes lacking green coloring matter. The
grouji inchnles mushrooms, molds, yeasts and bacteria.
PHYLUM II. Hryophytes (Bryophyta) : Plants without flowers and fruit. Green
Mostl)' with simj)le stems and roothke and leaflike parts. Small and incon-
spicuous.

PROBLEM 2. The Kinds of Fhmts of the Earth 91

Class i. Liverworts (Hepaticae): Sonic liave a sonicwivat branched, ribbon-
like structure flat on the ground, with simple rootlike parts. Others have
stems and rootlike and leaflike parts.

Class 2. Mosses {Musci): Erect. More complex in structure with stems, leaf-
like, and rootlike parts.
PHYLUM III. Pteridophytes {Pteridophyta): Plants without flowers and seeds.

Green. True leaves, roots, and stems with conducting tissue much like that

in higher plants.

Class i. Ferns (Filicinae): In temperate zones, mostly small with horizontal
stems. Spores borne on leaves or modified leaves.

Class 2. Horsetails (Eqiiisethiae) : Few species. Jointed stems with leaves
reduced to scales. Spores in conelike structures. Stems harsh to touch.

Class 3. Club Mosses (Lycopodinae): Few species. Creeping herbs with
erect stems bearing conelike structures with spores.
PHYLUM IV. Spermatophvtes {Speriiiatophyta) : Producing flowers and seeds.

Practicalh" all are green. Vary in size. Complex structure.
SUBPHYLUM I. Gymnosperms {Gyi}mosperi)iae): Woody plants with naked

seeds born on surface of cone scales. Mostly needle or scalelike evergreen

leaves. Includes the conifers, ginkgos and cycads.
SUBPHYLUM II. Angiosperms {Angiospermae) : Seeds develop enclosed in a

fruit.

Class i. Monocotyledons: Usually parallel veined leaves. Flower parts in
three's. Single cotyledon in seed.

Class 2. Dicotyledons: Netted veined leaves. Flower parts mostly in two's,
four's, or five's. Two cotyledons.

Questions

1. Why is it incorrect to use the words plant and flower as though they
meant the same thing? Into what tw^o large groups can all plants be
divided? In which group are trees and grasses placed?

2. What name is given to the division of flowerless plants that includes
the simplest plants? What are the characteristics of the plants in this
division? What name is given to the simplest plants that are green?
What do you call those without green color?

3. Describe a simple water-dwelling alga and two land-dwelling forms.
Do most algae live on land or in the water?

4. Are mushrooms algae or fungi? Give some interesting facts about
mushrooms.

5. Describe the common breadmold. What is mildew?

6. What is a lichen?

7. Tell about the yeast plant: its size, how it looks, how it lives, of what
importance it is to us. Define fermentation.

8. What is your idea of the size of an ordinary bacterium? What might
you see if you examined bacteria under the microscope? What is
their importance to us?

9. Which common plants can be classified as Bryophytes? How^ do these
plants differ from the Thallophvtes? How is Sphagnum moss used?

10. In general, where do ferns grow and how do they look? What was
true of these forms in ages past?

92 The Living Thifigs of the Earth unit

11. What are the characteristics of the spermatophyte? Define the words
herb, shrub, annual, biennial, and perennial.

12. What are the two main groups of flowering plants? How do they
differ?

13. Bv ^\•hat other names are the cone bearers known? How do they
differ from one another aside from the difference in the cones? In
what ways do we use the cone bearers?

14. Into what two groups are the true flowering plants subdivided? How-
do the leaves of most dicots differ from the leaves of most monocots?

15. List small monocots that are an important source of food for us. List
two monocots that are trees.

16. Define deciduous. What do foresters and lumbermen call the decid-
uous trees? List five families of deciduous trees that are widely spread
through the United States. What is true of the flowers borne by most
of these trees?

17. What similarity is there between the species included in the rose
family? List one or more herbs, shrubs, and trees that are grouped in
this family.

18. List some common relatives of the clovers. Of what importance are
they?

19. List other families that include food plants. Mention the names of
plants in each. List members of the mint family. What is character-
istic of their stems?

20. From what part of a plant is rubber made? What uses are made of
the cotton plant? Of the flax plant? Explain the importance of the
madder family.

21. What is true of flowers in the composite family? List several com-
posites that are familiar as weeds or as food plants.

22. Review briefly the groups of plants you have studied, starting with
the simplest and ending with the most complex.

Exercises

1. If you have the use of a microscope you will enjoy exploring water
collected from the surface of various ponds. You can easilv recognize
Spirogyra, and \()u will find a number of other threadlike plants. The
kind of green alga that grows on tree trunks is Frotococciis. Scrape
some onto a slide; tease apart the material you gathered; mount it in
water. How docs this plant differ from Spirogyra?

2. Stuch the common field mushroom, Agariciis. This can be bought
in the niarl<crs dining most seasons of the year. What do you find on the
lower side ot the cap?

3. To become ac(]uainted with various kinds of molds all you have
to do is Icaxc food exposed and they will come to you by themselves. On

PROBLEM 2. The Kinds of Plants of the Earth 93

pieces of moist white blotting paper in bowls, expose some bread, apple,
lemon, cheese, and other kinds of food. Cover the bowls and keep them
at room temperature. Keep the blotting paper moist. After several days
begin to observe closely at short intervals. Describe what you see. Com-
pare with the results obtained by your classmates. Do certain kinds of
molds seem to grow best on certain foods.^ Where do the molds come
from .5

4. If you crumble a small piece of yeast cake into water and mount a
tiny drop on a slide, you will be able to see the yeast cells under the
microscope. A magnification of about 400 times is necessary.

5. How can you find out whether or not there are yeasts in the air?
Plan the experiment. Discuss your plan with your classmates and teacher
to make sure you are on the right track.

6. If examples of mushrooms, mosses, ferns, lichens, horsetails, and
club mosses are available, examine them. Can you tell them apart? How.^
In some cases it may be difficult for you to decide whether or not they
are plants without flowers unless you see them at all times of the year.

7. Divide the class into committees, each of which will report on one
of the major divisions of the flowerless plants. Special reports would be
made by those who have raised molds or completed other projects. You
will then as a class have summarized the text on flowerless plants and you
will have made a small beginning toward learning to know the plant
kingdom.

8. Obtain examples of parallel-veined and net-veined leaves. Compare
and draw them. You can skeletonize leaves by soaking them in dilute
potassium hydroxide. Only the veins will be left.

9. Examine carefully some dicot flower, such as the sedum or sweet pea
or violet. (You will find a description of the flower under plant reproduc-
tion. ) Can you identify the parts? Compare with a monocot blossom.

10. Simmmry. Visit the vegetable market and make a list of the dif-
ferent plants seen. Perhaps several students could visit a florist shop and
list the flowering plants there. In class, see how many of the plants listed
you are able to classify into families. Now if you can sum up briefly
what you read about cone bearers, you will have summarized the pages
on "The plants with flowers and seeds."

Further Activities in Biology

1. Look through the titles of your state publications as well as those
of the United States Department of Agriculture for bulletins on mush-
room growing. Send for some and report. If you have a cellar with the
right conditions you might try raising some.

2. Ferns are common and easy to press. When carefully mounted they
make beautiful specimens. They are relatively easy to identify.

94 The Livmg Things of the Earth unit i

3. Look up and report on an industry that makes use of cone-bearing
trees, such as papermaking or the making of varnishes.

4. Make an evergreen collection for the class museum. iMount and label
a small branch and, if possible, a cone from each kind of evergreen that
you can find.

5. Start a collection of leaves of trees. Add descriptions of everything
you note about each tree.

6. Instead of pressing the leaves you can make blueprints or spatter
prints.

7. When you know your trees a tree map of the streets of your city
or town can be made.

8. It is interesting to make a collection of different kinds of woods.
You will need tools for smoothing and finishing to show the grain of each.

9. It is interesting to learn how to identify trees during the various
seasons of the year. By using a good tree book you can find out the
names of nearby trees and follow them throughout the year. If there are
trees on the school grounds, why not ask the shop teacher to help you
make neat metal signs with the names?

10. You can learn the names of the common spring, summer, and au-
tumn flowers by using a flower book.

PROBLEM 3 Hcnv Ai'e Living Things Named and

Classified?

The variety of living things. If you and

your classmates were to name all the
different kinds of living things that you
could remember you would probably
have a list with hundreds of names. Yet
as you know from reading Problems
I and 2 your list would represent only
a small part of the number of different
kinds of living things that biologists
know. Actually, more than one million
different kinds of living things have
been named and described by biologists.

The need for classifying. In order that
anyone may have even a slight knowl-
edge of so many different kinds of plants
and animals they must be arranged in
groups. Then, by learning the groups in
which they are arranged a person can
have an understanding of one million
plants and animals without knowing the
names of more than a few hundred.
Such a grouping of a large number of
objects in an orderly way and according
to some definite arrangement is called
a classificatioji. You know that plants
and animals have been classified, for in
the earlier problems you learned some-
thing of this classification. Let us look
more closely into the methods of clas-
sifying.

How all kinds of objects can be classi-
fied. If your hobby is collecting stamps,
you put together in one place in the
album all the stamps of one country;

you classify your stamps by putting to-
gether those that are alike in some easily
recognizable \\'ay, some characteristic.
In classifying stamps the characteristic
in which the stamps in any group are
alike is that they were printed for the
same country. Coins, too, may be classi-
fied in this way. They may be grouped
as English, French, United States coins,
and so on.

But if you have large numbers of coins
to take care of you do not stop when
you have grouped them according to
their countries. You find that the United
States coins are not all alike. Some may
be pennies, some nickels, and some dimes.
So you group them according to their
value. In other words, you now make a
further subdivision by using another
characteristic: the value of the coin. But
you can go still further in your classifi-
cation. You can subdivide the pennies,
for example, according to the date of
issue. You will find Exercises 1,2, and 3
useful for an understanding of classifi-
cation.

By looking at the diagram of one coin
collection you will see that the first
groupings are few in number; there are
only three groups according to countrv^
But when you come to the final group-
ing the groups are very numerous. Only
a few groups of the many possible ones
are shown in the diagram, Figure 126.

The Living Thijigs of the Earth unit

no Coins

60 U.S. Coins

Fig. 126

The diagram shows you something
else. The oftener you subdivide, the
smaller the mimber of specimens or in-
dividuals in each successive grouping. For
example, you start with 1 10 coins but the
number of United States coins is only 60.
In the next grouping there are 16, 14, and
30. And of the 16 dimes, divided accord-
ing to the year they were coined, how
many do you count in each pile?

Another important fact to understand
about every classification is this: the
specimens in the first subdivision have
few characteristics in common. For ex-
ample, the 60 United States coins form
a group of considerable variety; they
arc alike in two respects only, they are
metal coins and thev^ are United States
coins. But specimens in the final sub-
division have many characteristics in
common. For example, the three pennies
in the final subdivision are alike in beinir
metal coins, of the United States, being
made of "copper," having the same size,
the same color, the same value, and lastly
being of the same age. It should not sur-
prise you that this group contains fewer
specimens. Thev mu.st be matched in

many details before they can be fitted
into this group.

The classification of plants and animals.
It is relatively easy to classify stamps and
coins. But plants and animals are so much
more complex that their classification is
much more difficult. More than two
thousand years ago the great Greek
scientist and philosopher, Aristotle, wrote
detailed and accurate descriptions of
many animals. In doing this he came to
recoonize that certain ones had similar
characteristics. For example, he put rep-
tiles, birds, and fishes together into one
group, the egg-layers. You will remem-
ber from Problem i that we no longer
classify or group together animals on
the basis of laying eggs. We use other
characteristics.

As biologists continued their studies
they found that they were continually
obliged to change the classification be-
cause new facts were discovered about
the animals and plants then known, and
new plants and animals were being dis-
covered. The simple systems of classifi-
cation originally used were no longer
satisfactory. As a matter of fact, changes

PROBLEM 3. Living Things Are Na?ned and Classified

Fig. 127 i/.'f t'crsiiVi cat, the leopard, ajid the pmiia are placed in the same genus be-
cause of their si7>iilarity. However, they differ from each other, too. For this reason
each is placed in a different species, (national zoological park)

in the details of classification are still be-
ing- made as new facts are discovered.

Just as it becomes necessary to make
more and • more subdivisions in coin or
stamp collections when you get more
specimens, so with plants and animals
the first large groups had to be subdi-
vided further and further. Of course,
this was not all done at one time nor by
one man; many contributed. But a more
complete scheme than had appeared be-
fore was developed and established by
Carolus Linnaeus (1707- 1778). Linnaeus
did two important jobs: he established
a system of classification and he estab-
lished a new method of naming plants
and animals. To find out something
about Linnaeus, do Exercise 4.

Naming in the early days. Centuries
ago plants and animals were known only
by common names. This is sensible
enough for local everyday discussion but
it does not work for a biologist, for
sometimes the same animal or plant goes
by different names in different parts of
the country and sometimes the same
name is used for different animals or
plants. For example, in this country, to-

day, the common name "gopher" is used
for several kinds of ground squirrels in
the west, means "tortoises" in the far
south, and is applied to a snake in the
southwest.

To avoid this difficulty biologists
formerly wrote a long description of an
organism and used that for the name.
The more they knew about an organism
the longer the description; sometimes it
was four or five lines long. This did not
make matters simple.

Linnaeus named many animals and
plants. Linnaeus' scheme provides a short,
simple name for every organism; this
name may also partly describe the or-
ganism. Let us see how the system works.

Certain animals such as cats, lions,
tigers, and leopards are plainly much
ahke, so Linnaeus put them together in
a group called a gemis (jee'nus — plural
geiiera — ]en^er-a) . In the same way he
grouped wolves and dogs together in
a second genus. He did this for all the
kinds of animals and plants he knew,
finally arriving at many, many genera.
The subdivisions of a genus he called a
species (spee'shees). Thus there would

The Lk'iiJg Things of the Earth unit i

lui. 128 Coyote, (n. Y. zouLOGicAL socilty)

1- l(j. 130 Lcillic. ^UNII'EU STATES BURE-\U OF ANI-
MAL industry;

Ki(.. 131 RcJ fox. The rc'J {ox l>elov\^s to the
i^entis Vilifies. All the av'mials on this paire be-
long to the same fay/iily. (iiuc;ii davis)

Fig. 129 Dingo. The coyote, the dingo, and the
collie. Figure 130, belong to the smne gemis,
Canis. How do all three differ from animals in
the genus Felis?

he a cat species, a lion species, and a
leopard species within one genus. Then
Linnaeus named each genus. For example,
the genus Felis (feel'is) includes such
animals as cats, lions, leopards, and tigers.
The genus Canis (can'is) includes dogs
and wolves. Then each kind of animal
w as given as its first name the genus
name and as its second name a special
species name. The cat is Felis doi?iestica;
the lion, Felis leo; the dog. Cams
familiaris.

Now this is a very clever scheme.
Once you know that the dog is Canis
\aimliaris you know that any animal with
the first name Canis must be doglike.
Have you ever heard of the dingo? No?
Well, its name is Canis dingo. You would
not have to look at Figure 129 to kno\\
in a general way how it looks. And the
puma is Felis cougar. Again the name
rclls you a great deal about the puma.
Do Exercise 5 to see whether you under-
stand this. You may find Exercise 6 in-
teresting.

PROBLEM T,. Livifiif Thifigs Are Nauied and Class! Tied

Fig. 132 Polar bear. Polar and black bears be-
long to the sai7ie fa?!?ily but differe7it genera.
Bears, dogs, and foxes belong to one order, Car-
nivora. (national zoological park)

Linnaeus did this for every plant and
animal he knew and biologists have ex-
panded and improved the scheme so that
now all organisms that have been named
have two names: a genus name and a
species name. Very rarely there are three
names but these exceptions need not
trouble you.

Linnaeus' scheme of classification. You
know that the lion species and the cat
species resemble one another closely;
they fit into one genus. In the same way
some genera resemble other genera
closely. The genus Vulpes, including
some foxes, and the genus Cmiis, includ-
ing the dogs, are two similar genera. Such
similar genera are put together, and this
new and larger group is called a family.
\'ulpes and Canis thus belong to the same
family. See Figures 1 3 1 and 1 30.

Similar families are put together into
a larger group called an order. See Fig-
ures 128-133. Orders that are alike are
included in a still larger group called
a class. Classes that have certain charac-

" ■^-']

^jh

< xv

J^^.l^^..^^^^...J^^iJ^^Ssi

Fig. 133 Black bear, (national parks, canada)

Fig. 134 Bighorn niotintain sheep. (American

MUSEUM OF natural HISTORY)

Fig. 135 Bison. Sheep and bison belong to dif-
ferent genera bitt to the same fa7iiily. How are
they alike? (u. s. forest service)

too

The Living Things of the Earth unit i

ANIMAL KINGDOM

There are many other phyla

Phylum CHORDATA
Subphylum VERTEBRATA

The other classes include
bircis, reptiles, amphibia,
and fishes

Class MAMMALIA

There are about 19
orders among
mammals
alone

Order RODENTIA

There are 8 other
families in the
order Rodentia

Family SCIURIDAE

In this one family there
ore 9 other genera

Genus SCIURUS

^-^1

in this one genus
there are 8 other
species

Spec.es C4RO/./NENS/S

I"u;. 136 This chart shows how the gray sqtiirrcl fits into the aniDial kingdom. The
first subdivision is the phylum. Which subdivisions follow in turn? A chart that shows
how one animal is classified is simple; but, if you were to make a chart to include the
classification of all animals, you would need a sheet of paper at least as large as your
room. It would take you many years to do the job. (pinney from monkmeyer)

Living Things Are Named mid Classified ioi

PROBLEM 3,

teristics in common are grouped into a
phylum; phvla are grouped into a king-
dom. There are only tw^o kingdoms: the
plant kingdom and the animal kingdom.

All classification is the same in prin-
ciple. In describing the classification of
animals we began at the bottom with the
dog species and showed how similar
species may be grouped together to make
a larger grouping, a genus, and thus we
worked up to larger groupings and still
larger ones and finally to the animal
kingdom. In describing the classification
of coins we did the reverse. We began
at the top with the coin ^^k'mgdovi''' and
divided it into groups (corresponding to
phyla) and so on down until we reached
the final subdivisions into pennies coined
in a certain year. These would corre-
spond to species. Do you see that the sys-
tem is the same? Figure 136 will show
you how the animal kingdom is divided
first into phyla, phyla into classes, classes
into orders, orders into families, families
into genera, and genera into species.
Species are sometimes subdivided into
varieties or breeds. Thus you see how
the northern gray squirrel fits into the
animal kingdom.

As in the case of the coin collection,
the first large groupings are few in num-
ber; but the smallest subdivisions are
very numerous. There are only two
kingdoms and only about eleven phyla
in the animal kingdom but the number

of species runs to about 800,000. Further-
more, the larger the grouping the
smaller the number of characteristics
which the members have in common.
(See Fig. 126.) But when you arrive at
the smallest subdivision, the species or
perhaps the variety, the animals in such a
subdivision have a great many charac-
teristics in common.

The classification of plants. The classi-
fication of plants is not quite as clear
and easy to follow as the classification of
animals, but the principles remain the
same and the double naming is also used.
All maples, for example, belong to the
genus Acer (a'sir). One species from
which we get maple sugar is Acer sac-
chanmi. The red maple is Acer ruhrimi.
Every oak is called Quercus (kwir'cuss).
Quercus virginimm is the live oak of the
southeastern states. Quercus alba is the
white oak of the northeastern and cen-
tral states; and Quercus agri folia is the
coast live oak of California. Sometimes
there are slight but regular differences
between members of a species so that
we can make a further subdivision into
varieties. There are two varieties of red
maple. Each has a different third name
added to Acer nibrum.

A quick review of the summary tables
at the end of Problems i and 2 will help
you to remember the important facts
about animal and plant groups that have
been presented.

Questions

1. About how many different kinds of living things have been named?

2. What is meant by classification? Of what advantage is classification?

3. List the followinor characteristics in order of importance in grouping
coins: date, value, and country of coinage. Are the first groupings
or the last more numerous? In which grouping, first or last, are the

102 The Living Things of the Earth unit i

individuals most numerous? In which grouping, first or last, do the
individuals have most in common?

4. What two important contributions to the science of classification were
made by Linnaeus? When did he live?

5. Cite an example to show that common names for organisms are not
satisfactory.

6. Using the terms species and genus, explain the scientific name for a
cat and a lion. Which animal must Caiiis dingo resemble?

7. Starting with the final subdivision, species, list in order the larger
and larger groupings up to kingdom.

8. Contrast the number of species with the number of phyla in the
animal kinirdom. Which have more characteristics in common, all
the animals of one species or all the animals of one phylum?

Exercises

1. Why do not stamp collectors classify their stamps according to
color? What characteristics do they use?

2. Choose some group of common objects, such as automobiles (or
boats or houses), and prepare a list of characteristics by which vou could
subdivide them into groups and smaller groups.

3. All schools classify pupils so that they may be sent to the proper
grades, classes, and rooms. List the characteristics by which your school
classifies you. Be sure to take into account every item in your school
program. Can ^■ou think of other characteristics that your school might
have used?

4. Look up Linnaeus' life and prepare a report. Try to make him a
living person in your report. (See Singer, C, The Story of Living Things,
or Pcattie, D. C, Green Laurels.)

5. Following is a list of articles of furniture: table, chair, sofa, bed,
desk, bookcase, davenport, piano stool, bureau, and dresser. Add any
others that \ ou may think of. Classify these into genera according to
use (rather than according to size, shape, or where they are found). How
many groups or genera will you make? Compare with the answers of
your classmates. You may be interested in making up a double name
(genus and species) for each piece of furniture, as Linnaeus did for or-
ganisms.

6. Look back to Exkrcise 5. Could you gather these genera into fami-
lies? What cliarnctcrisrics did you use for putting them into the same
family?

PROBLEM 3. Living Things Are Named and Classified 103

Further Activities in Biology

1. With some help in the beginning you can learn how to construct a
key for some group of plants or animals. You might first make a key to
"key down" one of twenty or thirty assorted books on your bookshelves.
(Hint: The library uses a key.) Then collect leaves, shells, seeds, etc.,
and construct a key for each. Have some classmate try it in order to test
your skill.

2. Could you prepare a key for keying down each member of your
class? {Hint: How does the school classify pupils?)

In UNIT II you "will consider these problems:

Problem i . Of What Are All Living Things Composed?
Problem 2. How Do Their Activities Keep Cells Alive?
Problem 3. How Are the Cells Arranged in Animals and Plants?

UNIT II ALL LIVING THINGS ARE BASICALLY ALIKE

Vn:. 137 The sheep, the f^rass they eat, and the trees by the brook are very ii/uch alike
hi a great many ways. Can you explain in what ways they are alike}'

PROBLEM 1 Of What Are All Living Things Composed?

The structure of living things. All but

the smallest plants and animals are made
up of distinct parts which can be seen
with the naked eye. Plants may have
roots, stems, leaves. Animals may have
arms, legs, a head, and many other parts
visible from the outside. If we wish to
know their internal structures we dissect
them (cut them up). By doing this we
may see the heart, the stomach, the brain,
the liver, and many other parts.

Several hundred years ago the use of
magnifying glasses was learned by scien-
tists in Europe and the lejises (as they are
called) were improved so that they mag-
nified more than a hundred times. Then
men began to use them to discover just
how the parts of animals and plants are
constructed. They examined all kinds of
living objects: human skin, blood, parts
of insects, leaves of plants, stems, bark,
and so on. Robert Hooke (163 5-1 703),
an Englishman, was one of the first to
invent and to use a compound microscope.
He studied very thin slices of cork, which
is part of the bark of a species of oak
tree, and discovered that it was made of
little boxes. The walls of the boxes seen
by Hooke were thick. The boxes were
empty. He called the boxes cells. See Fig-
ure 138, page 106.

What is a cell? It is interesting that
Hooke was the first to call attention to
"cells" in living things but he never really

saw cells at all! The name "cell" has been
used ever since but it is now used for
something quite different from Hooke's
empty boxes. A true cell has been found
to be not an empty box but a tiny mass
of living matter. This material is difficult
to see because it is transparent and usually
almost colorless. Sometimes it can be seen
llo\\'ing; it is semiliquid. It was given the
name protoplasm. The protoplasm may
be surrounded by walls and it was these
walls that Hooke first discovered. He
failed to see the protoplasm itself because
the cork he examined was made up of cell
walls only. The protoplasm had disap-
peared.

As more and more parts of plants and
animals were studied it was discovered
that they were all composed of little
masses of protoplasm and that, very
often, there were no thick walls; the
protoplasm had the thinnest of walls
around it or no wall at all. These dis-
coveries were made over a period of
more than 100 years. Thus only grad-
ually did biologists come to realize the
comparative unimportance of the walls
and the importance of the protoplasm.
The name "protoplasm" was chosen for
the living- material because the word
means the first or most important sub-
stance.

The use of the microscope disclosed
two very important facts. The first was

io6

Living Things Are Basically Alike unit ii

Fk;. 138 A section through cork as seeji under
the vilcroscope. These are the structures which
Hooke named ''cells." Do these boxes seem to
be filled or etnpty?

that all living things are made up of
cells; the second was that cells are really
little bits of living substance, protoplasm.
The microscope. Before vou go further
into the study of the structure of living
things it is wise to learn about the in-
strument that has made this study pos-
sible. The modern microscope has been
described briefly on pages 10-12. It
would be well to read those pages again.
If microscopes are available in your
school you will learn how to use them.
Do ExFRCiSEs I, 2, 3, and 4.

^^'llat are the parts of a cell? There
are many different kinds of cells, very
different in shape and size. But each
cell is a tin\' mass of living matter called
protoplasm. When properly stained with
dyes and properly treated it can be seen
that each cell has three parts: the c ejl hod^ '
or cytoJ^liLim (sigh'toe-plasm) which is
the niain part of rlie protojilasm; a small
ball of denser protoplasm^ catted the
micleus (new'klee-us) lying within the
cell body; and a cell inemhrane (also
called plasma viembrane) surrounding
the cell bodv\ The cytoplasm, nucleus
and cell membrane are all protoplasm.
Thus these three parrs arc all living. If
you do FxTRrisi .^ you will see cells

Nucleus

Cell body

Cell membrane

Fig. 139 Cells like these are jound in the lining
of your mouth. What are the three parts of such
cells? How are they different from plant cells?
(See text below and Figure 140.)

from your own body which like all other
cells have the three parts just mentioned.
Plant and animal cells are fundamen-
tally alike; all have a cell body of cyto-
plasm, a nucleus, and a cell membrane.
There are some differences between
plant and animal cells, however. In most
plant cells the cytoplasm builds up a
firm cell wall of lifeless material outside
the membrane. This lifeless cell wall
usually consists of a tough, transparent
substance, cellulose (celPyou-lohss), or
an even harder woody material. Do Ex-
ercise 6 in order to see some plant cells.
By doing Exercise 7 you will see that
the wall of the plant cell is distinct from
the cell membrane. Plant cells differ
from animal cells in other ways, too.
Usually, they have one or more large
bubbles of liquid lying in the cytoplasm.
These are called vacuoles (vak'you-ohls).
Vacuoles are rarely found in animal
cells. A third difference between plant
and animal cells is that some of the cells
of green plants contain small bodies
called cbloroplasts (klor'oh-plasts). These
contain a very important green sub-
stance, chlorophyll, of which you will
read much more later. To help you with
this paragraph do Exercise 8.

PROBLEM I . The Couiposition of Lhing Things

Cell membrane

107

•Cell body (cyfop/asm)-

Nucleus {nucleoplasm)-

Animal

Fig. 140 (above) All cells have three d'niicn-
sions. In the animal cell as in the plant cell there
are two kinds of protoplasju. What other parts
does the plant cell have?

Fig. 141 (right) Cell from root tip of Trades-
cantia plant. What are the parts of this plant
cell? Which parts are livijig? Which are life-
less? Conipare this typical plant cell with the
mouth lining cells of Figure 1^9.

The nucleus of the cell. Cell bodies
are of many different shapes but nuclei
are all much alike in shape and structure.
In many cells they lie near the center
of the cell with cytoplasm all around.
Every nucleus has its own nuclear mem-
brane which separates it from the cell
body. The protoplasm of the nucleus is
denser and less liquid than the protoplasm
of the cell body. By means of micro-
needles used with the aid of a powerful
microscope the nucleus can be pulled
out of a cell. This shows that it is of

Plant

Vacuole
Cell wa

Cell body
(cyfoplasmj

Cell membranes

leolus

Vacuole

firmer consistency than the cytoplasm.
All nuclei contain a special substance
that differs from other substances in the
cell in that it stains deeply with certain
dyes. Because of this substance a stained
nucleus shows up clearly under the mi-
croscope. The living unstained nucleus
is difficult to see. The material that takes
the stain is present in a network or as
scattered granules; it is called chro-
matin (crow'mat-in). You will read
much more about chromatin later, for
the nucleus with its chromatin plays a

io8 Livmg

very important part in the life of the
cell and of the organism.

Frequently one or more small round
bodies are found within the nucleus.
They are called micleoU (new-klee'o-
lie; singular, nucle'o-lus). The nucleolus,
too, is readily stained. We do not know
what work it does in the cell.

The structure of protoplasm. You read
above that cytoplasm appears through
the microscope to be a thickish liquid,
colorless or light grey in color, contain-
ing small particles or granules, and that
the nucleus looks much like it, only
denser. Exercise 9 will be helpful now.
Staining protoplasm with dyes has helped
somewhat to bring out its structure but
no one can be certain that the stain has
not caused changes or produced sub-
stances not present in the unstained pro-
toplasm.

Although it seems to be comparatively
simple when seen through the micro-
scope experiments have shown that pro-
toplasm is really a very complicated
mixture of many substances. Some of
these substances are dissolved in water.
Some cannot dissolve in water and they
form what is called a suspension. (Raw
white of &^^ is a good example of a
suspension.)

The important fact about protoplasm
is that it seems to have a very definite
and complicated structure and it keeps
this same structure, in general, as long
as it remains alive. High or very low
temperatures, dryness, or other changes
in the surroundings, of course, may kill
it.

Of what is protoplasm composed? 1 he
studv of substances, their composition
or make-up, is called chemistry. To find

Things Are Basically Alike unit ii

Fig. 142 The 12 most common elements in plant
and animal protoplast)!. Calcium (Ca), sodium
(Na), and chlomie (CI) are not always present.
Symbols are explained at the bottom of this
cohnmi. Which fojtr elemefits are present in the
largest anioimts? What proportion of proto-
plas?n is oxygen? Percentages are calculated by
weight.

out what substances make up protoplasm
biologists have used the methods devel-
oped by chemists for their own experi-
ments. For example, protoplasm has been
treated with chemical substances, and
many other types of experiments have
been performed.

Among the first things learned was
what elements are present in protoplasm.
An element, you may remember, is one
of about 98 relatively simple substances
of which all other substances in nature
are made. Everything in our world, liv-
ing and lifeless, consists of one or more
of these elements. The elements are often
represented by symbols \\ hich are abbre-
viations either of the present name or of
some name used in the past. Perhaps you
already know that the symbol for oxy-
gen is O and that for iron is Fe. The
following elements are found in all pro-
toplasm: carbon (C), oxygen (O), ni-
trogen (N), hydrogen (H), sulfur (S),

PROBLEM I. The Co?npos'ition of Livmg Things

109

Fig. 143 Dr. Walter S.

Ritchie of the University of
Massachusetts is study i7ig
some of the coijipoiinds
found in protoplasDi. (uni-
versity OF MASSACHUSETTS)

phosphorus (P), iron (Fe), potassium
(K), and magnesium (Mg). Many other
elements have been found in some pro-
toplasm and traces of certain others may
be present in all protoplasm.

Compounds in protoplasm. The ele-
ments in protoplasm are usually not
found as elements but are combined
chemically to form substances known
as compojijjds. Compounds are chem-
ical combinations of elements. When
elements combine chemically they form
a new substance which is different from
the elements that make it up. podium.
f or ^ exam ple, is a metal that would b urn
your skin if you touched it, and chlorine

ggmbj ii e^ ch e m icaJIyL f orm-
ing water, a compound \vhi ch has very
different properties from eithe r hydro-_
gen 'or oxygen. And so with all other
elements; when they unitg_jdiemically

they loG G i h o ir clu racteristics and some-

thirfg new appea?S. Yuui"~feaclier can
perform ExercIISE KO so that you can see
for yourself how the characteristics of
elements disappear when they combine
and form a compound. Compounds
themselves combine chemically with each
other and when they do they form new
compounds with definite characteristics.
There are many different compounds
found in protoplasm but there are only
a few that are always present. The most

is a poisonous gas. i hese two substances
rnmhvmpT^^Hiiiw-ijllyj^na]^ a r-n^^ ppun^- — abundant of these is water; it forms a
thatis called sodium chlo ride or ordinary la rge part of all protoplasm. Other corn-
table salt. The two gases, hydrogen and pounds are salts like sodium chloride.

no Lwing

Both water and sodium chloride are com-
pounds that, as you know, are found
in nature outside of Hving matter. But
there are other compounds in protoplasm
that are made by protoplasm and that are
never found in nature outside of living
things; all of them are organic com-
pounds. In both plants and animals, we
find that the most abundant organic com-
pounds are the sugars, the starches, the
fats, and the proteins.

Sugars, starches, fats, and proteins.
Sugars and starches are much alike; they
are grouped together as carbohydrates.
All of them contain only three elements,
carbon, hydrogen, and oxygen; and the
hydrogen and oxygen are always in the
same proportion as they are in water,
that is, t\\'o parts of hydrogen to one
of oxygen. The chemical formula for
a common simple sugar is C.iHi.O,.,, the
formula for starch is QiHjoO^. (The
chemist would write it (QHioOg)!).)
Cellulose, the material found in plant cell
walls, is also a carbohydrate.

Fats, too, contain the elements carbon,
hydrogen, and oxygen; yet fats are dif-
ferent from carbohydrates. Fats have
fewer oxygen atoms in proportion to
the hydrogen than carbohydrates have.

Proteins are different from both fats
and carbohydrates in this respect: they
always contain the element nitrogen.
Proteins often have sulfur and other ele-
ments as well. They are much more
complicated chemically than are the car-
l)oh\drates and fats. Proteins arc essential
for the making of protoplasm.

Tests for the compounds in proto-
plasm. It is easy to detect water, min-
erals (salts), starches, certain kinds of
sugars, fats, or proteins in living things.

Things Are Basically Alike unit ii

Fig. 144 When sulplmric acid {H„SO^) was
added to the sugar, the dark mass of carbon was
produced. What does this tell us about the com-
position of sugar? ( Sullivan)

You can do so because a test has been
discovered for each of these substances.
For example, after much experimenting,
it was discovered that when iodine solu-
tion and starch are mixed a substance
with a deep blue color is produced. Only
starch behaves this way with iodine so-
lution. Therefore, iodine solution is a
testing^ agent for the presence of starch.

In the same way tests have been dis-
covered to indicate the presence of
simple sugars, proteins, fats, mineral mat-
ter, and water. Finding these tests was
a difficult task, but applying them is an
easy matter. If you follow the directions
in ExKRCiSES II, 12, 13, 14, 15, and 16
you will be able to discover for yourself
how the tests work. Later you will test
parts of plants and animals for the pres-
ence of these substances in protoplasm.

What arc mixtures? You have read
rJiat protoplasm is a complicated mixture
of substances. It is important that you
understand what is meant by a vfixture.
By doing Fxfrcisf. 17 you can get a clear

PROBLEM I

The C 07/1 posit ion of Living Things

1 1 1

Fig. 145 Particles of sugar are shown as trian-
gles, particles of water as circles. According to
this picture does sugar water seem to be a coin-
pound or a mixture? Explain.

understanding of what chemists mean
by a mixture. It differs from a compound.
Often when two or more elements are
put together they do not unite chemi-
cally. In this case they do not form a
compound. Instead they form a mixture.
In a mixture each element keeps its own
characteristics. In a compound where
chemical combination has taken place
the elements lose their special character-
istics. A4ixtures may be combinations of
compounds, or elements; or they may
be combinations of compounds and ele-
ments together. But the important thing
to remember is that the substances that
go into the mixture do not lose their
characteristics because they do not com-
bine chemically with one another.

Protoplasm is a mixture of compounds
and elements, each substance retaining
its own special characteristics because
it does not combine chemically with the
other substances near it. To test your
understanding of the chemistry you have
learned, do Exercises 18 and 19.

What have you learned? Let us review
all you have learned in this problem.
Plants and animals are made up of tinv
invisible structures known as cells. All
cells, normally, are alike in having three
parts: a cell body or cytoplasm, a nu-
cleus, and a cell membrane. These parts
are all living and can be called bv the
general term protoplasm. The nucleus
is denser protoplasm than the cell bod v.
It contains a substance called chromatin.

But plant cells often have structures
which animal cells do not have. Almost
always they have a cell wall of a lifeless
material called cellulose. They usually
have one or more vacuoles filled with
liquid. And many of the cells in green
plants have chloroplasts which contain
the green coloring matter known as
chlorophyll.

Protoplasm seems to be a thickish
liquid, colorless, and containing small
granules. Little is known about its struc ■
ture, but we do know of what substances
it is composed. Chemists who study the
composition of substances define ele-
ments as comparatively simple substances
of which all other substances are com-
posed. They tell us that the elements
which regularly occur in protoplasm are
carbon, hydrogen, oxygen, nitrogen, sul-
fur, phosphorus, iron, potassium, and
magnesium. But these elements are for
the most part found united chemically
with each other in the form of com-
pounds.

Some of the compounds found in pro-
toplasm, such as salt and other mineral
compounds, are found in nature outside
of living matter. But some of the com-
pounds found in protoplasm are never
found outside of living matter, except

1 1 2 Livm^ Things Are Basically Alike unit ii

as man extracts them from living matter, acteristics and you can discover the

These compounds which are made by various compounds in protoplasm by

protoplasm are proteins, carbohydrates applying the appropriate tests,

(starches and sugars), and fats. Thus you have learned what makes

Protoplasm is a mixture of these vari- up all living things, whether plants or

ous compounds; in other words the com- animals; and you have seen that in their

pounds are not chemically united with structure plants and animals are funda-

one another in the living stuff, proto- mentally alike. Both consist of the com^

plasm. Therefore they keep their char- plex mixture, protoplasm.

Questions

1. What can you say about the internal structure of many animals?
About when did men begin to examine the parts of animals and plants
more closely? What did Robert Hooke discover?

2. What is a cell? What is protoplasm? Why did Hooke not see proto-
plasm? State the two important facts that were disclosed by the use
of microscopes?

3. Name, locate, and describe the nine or ten parts of the microscope
with which you must be familiar in order to use it correctly. What
are the rules for the use of the low power? What is meant by the
words "focus" and "field of vision"? How does a compound micro-
scope differ from a simple microscope?

4. What are the three main parts of an animal cell? What three struc-
tures are commonly found in the cells of plants but not in the cells
of animals? How does a cell membrane differ from a cell wall? What
is cellulose and where is it found?

5. Describe the structure of the cell nucleus. What is the important
material found in everv" nucleus?

6. What arc the characteristics of protoplasm? What is known about
the structure of protoplasm?

7. With what does chemistry deal? What is an element? What nine
elements are found in all protoplasm?

8. What is a compound? Using table salt as an example explain what
happens to elements when they unite chemically w ith one another.
What four compounds are found in protoplasm and not in nature
outside of living things? What two compounds are classed as carbo-
hydrates? What is true of the chemical composition of all carbohy-
drates? How tlo fats and proteins compare with carbohydrates in
their clicniical composition?

9. What is the test for each of the following: starches, simple sugars,
fats, proteins, water, mineral compounds?

10. How docs a mixture differ from a compound? Is protoplasm a mix-
ture or a compound?

PROBLEM I . The Co7n position of Living Things

113

Fig. 146 The lenses below
the stage are not usually at-
tached to high school micro-
scopes. When you look
through the microscope you
7ise two sets of lenses. Each
set consists of two or more
separate lenses. Can you find
the sets? This jnicroscope
is cut through the middle.

(BAUSCH & LOMB OPTICAL CO.)

1 1.

In review state briefly what you have learned in this problem about:
{a) Cells, explaining the diflferences between plant and animal cells.
(b) Protoplasm, its characteristics and the elements of which it is
composed, {c) The compounds which are mixed together in living
matter, {d) Why plants and animals are said to be fundamentally alike.

Exercises

1. If you will have an opportunity to use a school microscope you
should be familiar with its parts. Starting at the bottom they are: base;
mirror; diaphragm (attached to the bottom of the stage); stage (which
holds the glass slide); arm (the part by which you carry the microscope);
barrel (the thick vertical tube); 7wsepiece (revolving part at the bottom
of the barrel); objectives (two or more lenses screwed into the nosepiece);
coarse adjiistDiem (two large wheels on either side of the barrel); fine
adjiistviejU (two smaller wheels); ocidar or eyepiece (the lens fitted into
the top of the barrel).

1 1^. Living Things Are Basically Alike unit ii

Examine the mirror. In which directions can it be moved? Note that it
has a flat and a concave (hollowed out) surface. Turn the concave surface
toward the light. How do the two objectives differ from one another?
The shorter one is the low-power objective. Examine the diaphragm care-
fully. How does it work? What is it for? Slow ly turn the coarse adjustment,
then the fine adjustment. What effect does each have on the barrel? If
the microscope is placed before you so that the arm is toward you, how
must you turn the wheels in order to move the barrel up? It is important
that you remember this.

z. How to find an object under the low power: {a) Place the micro-
scope so that the pillar is toward you wath the base resting firmly on the
desk or table, {h) Place the slide on the stage so that the material on the
slide is over the hole in the stage. If the object is small, it must be centered
over the hole. Hold the slide in place with the uvo clips, {c) Turn the
low-power objective (shorter one) until it clicks into place. It ^\'ill then
be exactly over the hole in the stage, {d) With your eyes held at the
level of the stage, not at the ocular, lower the barrel, using the coarse
adjustment, until the tip of the low-power objective is about one fourth
inch above the stage, {e) With your eye at the eyepiece turn the mirror
so that the concave side is up and secure the best uniform bright light
by moving the mirror, (f) Now, with your eye at the eyepiece, slowly
raise the barrel by turning the coarse adjustment toivard you. Do this
until \ ou can clearly see the material on the slide, (g) You may have to
ni()\'e the slide to see some other part of the object. (/:?) If the object is
not as clear as it might be, turn the fine adjustment no more than a single
revolution, now one way, now the other, to see whether you can focus
more accurately. If you still do not get a satisfactory focus, try once
more from the beginning, this time focusing more carefully ^\•ith the
coarse adjustment before using the fine adjustment.

3, To focus, using the high power: {a) With the concave surface still
on top move the mirror until the best light is obtained, {h) Focus care-
fully under the lo-xo power. Make sure that the object you are looking at
is in the center of the circle (field of vision), (c) By grasping both ob-
jectives, slowly swing the high-power objective into position over the
hole in rhc stage without shaking or moving the microscope, (d) With
your eye at the eyepiece, move the fine adjustment toward you slowly
until the object becomes clear. Use only the fi7ie adjustment. If instead of
becoming clearer it becomes less clear, turn the fine adjustment the other
wa\-. Bur do not make more than one fourth of a revolution with the
fine ;uljustnicnr.

4. 1 he magnidcd image, ^'ou can learn some important facts about the
image you see through the microscope by preparing a slide of a small
piece of newsjirinr containing the single letter "c." Place the slide so that
the letter is upiighr, as you read it. After you have focused under the low
power, write in your notebook a statement that tells how the image is
tlifferent from the real letter. Now move the slide to the riohr wh.ile you

PROBLEM I . The Composition of Living Things 1 1 5

are looking through the microscope; then move it to the left. Now state
in your notebook what the microscope seems to do to the motion of the
object. With your eye at the eyepiece, move the object away from you
and then toward you. Describe in your notebook what you notice. Com-
pare vour statements with those of your classmates so that all can agree
on the best one.

5. How can you see the three parts of a cell? Mount some of the cells
of the lining of your mouth (mucous membrane). Gently rub the inside
of your cheek with a clean tongue depresser. Mount the material in a
drop of water on a slide, cover, and examine under high power. Stain
with dilute iodine solution (Lugol's). Find a place where the cells are
separated from one another. What structure now shows more clearly?
Where does the nucleus lie? Since you can see the nucleus in a cell of
three dimensions what characteristic must the protoplasm have? The firm
edge of the cytoplasm is the cell membrane; it shows as a line. Draw
and label several cells.

6. What is the structure of onion skin cells? Cut an onion lengthwise.
Separate some of the layers. With forceps peel off some of the thin skin
from the inner side of one of the layers. Mount a piece about one quarter
of an inch square in a drop of water on a slide. Lay a cover glass over it.
Examine under the low power of the microscope. If there are too many
black-rimmed circles (air bubbles) mount another piece. Compare with
the cells from the mouth studied in Exercise 5. How do the onion skin
cells differ? Draw what you see.

Now study the cells carefully under the high power. Permit a drop of
red ink or a weak solution of iodine to run under the cover glass. What
more do you see? Draw and label.

7. To see the cell membrane of a plant cell prepare cells of onion skin
mounted in a drop of weak salt solution. Use the low and high powers

^ of the microscope. What is happening within the cell? Can you see the
membrane? Why were you unable to see the cell membrane before?

8. Answer the following questions: {a) If you can see the nucleus in-
side of a cell what must be one characteristic of cytoplasm, cell mem-
brane, and cell wall? {b) Can you explain how your idea of a cell is quite
different from Hooke's? {c) What are the important facts given in the
paragraph on the structure of a cell? This will summarize a difficult para-
graph.

9. The structure of protoplasm. Use the high power of the microscope
to examine protoplasm in an ameba or a slime mold. What is the color
in bright light? What is the color in dim light? Is the color the same
throughout the organism? Do all parts of the protoplasm contain small
particles? Are you sure that all protoplasm looks like this? Explain.

10. Can you devise an experiment in which you get two elements to
combine to make a compound? (Hifit: Charcoal is almost pure carbon.
Carbon dioxide is a compound consisting of carbon and oxygen. You can
detect the presence of carbon dioxide because it turns clear limewater

1 1 6 Living Thi?igs Are Basically Alike unit ii

milky.) Can you put these same elements together without having them
combine? How?

1 1 . Try the test which has been discovered for detecting starch. Ob-
tain a water solution of iodine crystals and potassium iodide (Lugol's
solution). Add a few drops to a small amount of starch in water. Mix
the iodine solution with sugar, protein (white of an egg), fats (butter or
lard), table salt, and water. What is your result in each case? Why do
you add iodine to these other substances? Note that you have not re-
peated the chemist's experiment since you have not tried iodine with a
vast number of other compounds. Why can iodine be used as a test for
starch?

12. Trv the test which has been discovered for detecting simple sugars.
Dissolve some grape sugar (corn syrup will do) in water. Add either
Fehling's solution or Benedict's solution. Heat the mixture until it boils.
What is the final color of the substance? Do you get the color change
with any substance other than simple sugar? Why do you test these
other substances? Do your classmates get the same results?

13. Trv the test that has been discovered for detecting proteins. Mix
some of the white of an egg with dilute nitric acid. Boil the mixture for
a few seconds. (Careful!) What color change do you notice? Now add
ammonium hydroxide. What is the second color change? What else must
you do? Why?

14. Try the test for detecting fats. Rub a bit of butter on a piece of
unglazed paper. Hold the paper to the light. The spot that appears on
the paper is called a transhicein spot. Why? All fats leave a translucent
spot on paper. Do substances other than fats produce this kind of spot?

15. Try the test that has been discovered for detecting water. Boil
some water in an open dish. Hold a dry, cold glass tumbler over the
boiling water. What forms on the sides of the glass? Heated water vapor
condenses when it strikes a cold object. If you try this test on the other
substances you may get the same results. Explain.

16. Try the test for detecting mineral compounds. Trv to burn table
salt. Since minerals do not burn, at least not at the low temperature at
which other substances burn, they will remain as a white ash. What be-
comes of starch, sugar, fat, and protein when they are burned?

17. The difference between a mixture and a compound. Examine iron
filings and powdered sulfur. They are examples of elements. Describe
them. One property of iron is that magnets attract it. Siiow that this is
so. Now stir together some iron filings and sulfur powder until they are
thoroughly mixed. Apply the magnet. What happens? In stirring the two
elements together did a compound form or did you form a mixture?
Explain your answer. Next, heat in a crucible a small amount of iron
filings and powdered sulfur. After thorough heating apply the mac^net.
What happens? I'"xplain. This is a compound. Put into words what you
understand to be the difference between a mixture and a compound.

PROBLEM I . The Composkloii of Living Things 1 1 7

18. Is salt water a compound or a mixture? How can you find out?
Do this experiment at home.

19. Answer the following questions: (a) Are the gases oxygen, nitro-
gen, carbon dioxide, and water vapor, which make up the air, mixed
together or is air a compound? Give scientific evidence for your answer.
(b) The chemist speaks of water as HoO. What is the meaning of the 2
after H? Carbon dioxide is COo. What are the proportions of C and O?
Carbon monoxide consists of carbon and oxygen. The prefix "mon"
means one. Write the formula for carbon monoxide, (r) Ordinary granu- ,
lated sugar is C^.^rioX)^^. What do you know about its composition?

Further Activities in Biology

1. You can easily learn to prepare slides. Which is the best way of
putting on the cover glass so that bubbles will not form? Consult books
or ask your teacher for further help. In time you will probably want
to learn how to make microscope slides which are permanent. This is
difficult and takes patience.

2. Can you think of some way of making a model of a cell which will
give your classmates a good idea of how a cell really looks? (Do not for-
get that protoplasm is transparent.)

3. Prepare a report on the history of the microscope.

4. Prepare a demonstration other than that used in the text to show
how elements change their nature when combined into compounds.

5. Prepare a demonstration of the compounds found in living things.
Try to get many diff^erent examples of each class of compounds: many
starches, many sugars, and so on.

PROBLEM A Hoiv Do Their Activities Keep Cells Alive?

What do living things do to remain ahve?

This question might have been asked
another way: what is it that Hving things
do that makes them different from hfe-
less things? You can think at once of
many activities that distinguish the Hving
from the hfeless. If you think of animals
you will say they move from place to
place (without the help of an outside
agent) ; they take in food and grow; they
breathe; they produce many substances
useful to them; they get rid of wastes;
and they make more of their own kind,
or reproduce. Plants engage in many of
these activities, too, although sometimes
in ways different from animals. Trees
cannot move from place to place, but
they use food and grow, they make sub-
stances useful to them, and they cer-
tainly make more of their own kind.

Activities of the organism are activities
of the cells. You learned in the last prob-
lem that all living things are made up of
cells — small masses of protoplasm. There-
fore, it should not surprise you that all
the activities of a living thing are also
the activities of its cells. Food enters the
cells in your body, and the cells grow;
cells make substances useful to cells, and
they reproduce. It is true that most of
the cells in your body do not move from
place to place but the protoplasm within
the cell moves. Some of these activities
are visible when you study cells with

the microscope; others are not visible.
If microscopes are available, the move-
ment of protoplasm can be readily seen
in the ameba and also in some plant cells.
See Exercises i and 2. Living paramecia
can be seen engaging in various activi-
ties. See Exercise 3. But you must re-
member that the paramecium is a single-
celled animal and performs some of its
activities differently from the cells that
make up the body of a many-celled
animal or plant. Let us study in more
detail some of the more important cell
activities.

Oxidation occurs in the cell. Some of
you may know the meaning of the word
oxidation. All of you can guess from the
sound of the word that it has somethinij
to do with oxygen. Oxidation is the
chemical union of a substance with oxy-
gen. If carbon unites with oxygen the
compound that results from the union
is normally carbon dioxide. If hydrogen
combines with oxygen, the compound
hydrogen oxide (water) results. If iron
unites with oxygen, iron oxide (com-
monly called rust) is produced. And so
with other substances; when they unite
with oxygen, oxides are formed.

The union may be rapid or slow. You
constantly see examples of rapid oxida-
tion, for rapid oxidation is burning or
yombusrion. When you touch a lighted
match to a piece of paper, rapid oxida-

PROBLEM 2. How Cclls Keep Alive

tion (burning) usually takes place. The
paper unites with the oxygen which is
present in the air. In uniting, it forms
a variety of oxides and produces heat
and light. It is true that the paper does
not burn until you touch a lighted match
to it; the match serves to heat the paper
to its kindling temperature. This is gen-
erally necessary for rapid oxidation. Slow
oxidation occurs at lower temperatures.

There is another difference between
slow and rapid oxidation. In slow oxida-
tion no light is produced. But heat is
always produced whenever oxidation
takes place; the slower the oxidation,
the less the heat. In fact the amount of
heat may be so small that delicate instru-
ments are needed to detect it. At this
point, unless you have done these ex-
periments before, you will find it profit-
able to do Exercises 4, 5, and 6, Also try
Exercise 7.

Let us sum up what we have learned
about oxidation: Oxygen must be pres-
ent if oxidation is to take place; an oxide,
or^compound of oxygen with another
substance, is always formed; heat is re-
leased; and if the oxidation is rapid,
light is also produced.

Oxidation occurs in all living cells.
Some of the compounds in the proto-
plasm, particularly carbohydrates and
fats, unite with oxygen. Oxides are
formed in the cell and heat is produced.
Among these oxides is carbon dioxide.
Can you devise an experiment to show
that oxidation goes on somewhere in
your body? Do Exercise 8. Ordinarily,
in this oxidation within the cell no light
is produced. Oxidation within the cell
is of great importance. The whole proc-
ess is also called cellular respiration.

119

Fig. 147 Tlois l.yirdlfr is using energy. Where
does it come from? (public schools of evans-

VILLE, INDIANA)

Energy. What is energy? Energy can
be defined as the ability to do work,
that is, make something move. Energy
makes work possible. You just read that
when burning takes place heat and light
are produced. Heat is one form of en-
ergy; light is another. There are other
forms of energy, many of which are of
less interest to us in biology.

Let us consider for a moment why
heat is thought of as a form of energy.
In a simple machine like a steam engine
the engine cannot do work unless there
is steam to push the piston. You say,
therefore, that steam has energy, the
ability^ to do work. The energy in the
steam is heat energy. When the steam
loses its heat and becomes water again,
it can no longer push the pistons; that
is, it can no longer do work; it has lost
its energy. Light energy is not often
used by man for running machines; but

I20

Liv'mg Things Are Basically Alike unit ii

Fig. 148 Breaking up a log jcn/i. There are active cells in the viai and in the trees
along the bank. What activities are being carried on in these cells? In which cells is
there the greatest amount of oxidation? (American museum of natural history)

\c)u will learn more about light as an
important form of energy in a later unit.

You are acquainted with electrical en-
ergy, which can be transferred from one
place to another in wires. This form of
energy can be changed into other forms,
such as heat and light, or it can do work
directly as in causing a motor to turn.
You may have seen the inechajiical en-
ergy of moving water turn a Avaterwheel
or move a boat or e\en rocks in the
stream bed. It is easy to understand that
heat, electricity, and the mechanical en-
ergy of moving objects can do work.

iMicrgy, or the al)ilit\- to do work, may
be stored. Coal contains stored eneriry,
and, since this cncrg\- lies in the chemical
make-up of the coal, it is also called
che7fiical energy, in biology chemical

energy is of great importance; all living
things contain it.

All forms of energy can be changed
into one another. For example, when
coal is used for making steam in an
engine its stored chemical energy is
changed into heat energy; this heat en-
ergy is used in machines to produce
electrical energy which is turned into
light energy in the lamps in our homes
or into mechanical energy in our wash-
ing machines.

Oxidation in the cell changes stored
energy. You have learned that in all oxi-
dation heat energy is released. You just
read that when coal is burned the stored
energy of the coal is changed partially
into heat energy. The same thing hap-
pens in a cell. In a cell it is carbohydrates.

PROBLEM 2. How Cclls Keep Alive

fats, or proteins that are oxidized and
their stored chemical energy is released
as heat energy. You may wonder how
the coal and the living cells got the en-
ergy which is hidden within themselves.
The understanding of this is an important
part of biology. You will learn in the
next Unit how energy gets into all living
cells. For the present you need only re-
member that all living cells contain stored
chemical energy; this is changed into
other forms in the process of oxidation.

Work in living things depends on oxi-
dation in the cells. Have you ever
stopped to think that as long as an or-
ganism remains alive it is constantly re-
leasing energy? Heat is being released
and work is being done. To biologists
work means more than earning your
living or going to school. Playing ball is
much harder work than studying a les-
son. Moving your eyes across this page
is also work. To keep your body standing
upright you must do a considerable
amount of work. Even when you sleep
yout heart keeps working regularly; so
do the chest muscles and other parts of
the body. Millions of cells are always
carrying on oxidation and doing work.
In plants, too, the living cells are con-
stantly carrying on oxidation, releasing
energy, and doing work. All living things
do work as the result of the oxidation
which occurs in all their millions of cells.

Why oxidation can go on continuously.
You read that carbohydrates, fats, and
to some extent proteins in protoplasm
serve as fuel in living cells. These com-
pounds are spoken of as food substances
for living things. They unite with oxy-
gen and thus they disappear and new
compounds are formed. In other words

121

Fig. 149 This resting cow is doing work. What
kind of work is being dojte? What ki?ids of
energy are being released? (schneider and

SCHWARTZ)

the food compounds and oxygen are
constantl)' being used up in oxidation.
But, under normal conditions, they are
constantlv^ being replaced. Evidently,
there must be a fairly constant passage of
oxygen and of these various compounds
into the living cell. They move into the
cell by the process known as diffusion.
If you do Exercise 9 you will see diffu-
sion occurring. Let us review it.

Diffusion. You know that when you
put sugar into the bottom of a cup of
coffee and wait a short time the sugar
will sweeten all parts of the drink even
without your stirring it. That is, the
sugar moves through the coffee. But
how is its motion explained? Chemists
tell us that all substances consist of tiny
particles known as molecules (moll'e-
kewls). These molecules are in constant
motion. In gases the molecules are far
apart and they bounce about actively.
Each one moves, first in one direction.

122 Living Things Are Basically Alike unit ii

then in another. In liquids the molecules [T ~ ~J

are closer together; they move, but move l^^^^^^^M/ C

less actively than in gases. If two gases l^^^^^^^^l

are put together, the molecules of both f^^^^^^^^f

eases move actively and the gases inter- 1^^^^^^^/ B ItSni^^^-c^^^

mingle rapidly. If two liquids are put l^^^^^^^/--- —wi^" *""

together, the molecules of both liquids 1^^^^^^/

-1 i^MrolMWIal

usually move about and intermmgle, nQ9KR0l|

though more slowly. This intermingling i jlMMW^/ l^g^jgiil^/ II

of substances through the motion of their ^^^ ^^^ ^^^^^^ .noleades arc sbov^^n as nian-

molecules is called diffusion. Even in g/^^^ water ?nolecules as circles, hi 1, sugar mole-

solids the molecules intermingle or dif- cules {molasses) have just been put in ivith a

r 1 1 11. -.^A^^A dropper. II shows what has happened after a

fuse, but they move very slowly mdeed. " ^^ . ^Tr; ; i i ^L j

■ • •' short tt7/re. Why have sugar vwlecuies appeared

Do Exercise io. at level B? Compare the mmiber of water viole-

By using liquids which differ in color czdes at Level A in I and II. Explain. Draw the

you can actually watch them diffuse nmibler as it would look after longer standing.

' Draw it as it woidd look if half as viuch sugar

though, of course, you cannot see the j^^^ y^^^ ^^^^ ^.„

molecules. If you carefully put warm

molasses with a medicine dropper into oxygen are on the other side of the mem-

the bottom of a tumbler of warm water brane. The membrane seems to have no

and allow it to stand quietly you will openings. How can substances pass

soon see these liquids intermingling, through the cell membrane?

Each substance spreads or diffuses from Diffusion through a membrane.-'' A

the region where its molecules are close number of simple experiments can be

to one another (highly concentrated) to set up to find out whether liquids can

where its molecules are farther apart pass through a membrane which has no

(less concentrated). After some time the visible pores. To find out whether water

molasses molecules are no longer close can pass through a membrane, a sausage

together at the bottom; they have spread casing may be used as the membrane.

or become less concentrated. The same This is the wall of a pig's intestine; it is

is true of the water molecules; they have made of cells, although they are no

also spread, and eventually the two longer living. If sausage casing is not

liquids will have completely intermin- available a thin cellophane membrane

gled. Both liquids have moved. may be substituted. This also has no

Now food and oxygen move into all visible pores. The bowl of a thistle tube

the living cells by diffusion. But you may may be filled with a mixture of water

raise this objection: in the timibler there and molasses with the membrane tied

was nothing to separate the molasses securely over the mouth of the tube.

from the water; around the cell body The thistle tube may then be inverted

there is a membrane and the food and and its mouth placed into a tumbler of

Osmosis is often defined as diffusion through a membrane. However, osmosis
is variously defined and therefore, the authors think it better not to use the term at
all, especially since by any definition osmosis is diffusion under special conditions.

PROBLEM 2. How Cells Keep Alive

Sugar molecules
(triangles)

Water molecules
(circles)

Rubber
band

Membrane over end of thistle tube

Fig. 151 Sugar and water molecules are within
the thistle tube. Only water molecules are out-
side it. If only water molecides ca?i get through
the 7}iembrane, what will happen to the amount
of liqtiid ill the tube? What would happen if
both kinds could get through the meiiibrane?

tap water. Where are the molecules of
water more concentrated when the ex-
periment is set up? Remember more
concentrated means closer together, not
more numerous. Are the water molecules
more concentrated within the thistle tube
where you have some water mixed with
thick molasses or are they more concen-
trated within the tumbler filled with tap
water? Since the water molecules tend to
diffuse from where they are more con-
centrated to where they are less concen-
trated water should move from the
tumbler into the thistle tube provided
it can get through the membrane. If it
does get through the membrane how will
this become apparent after a short time?

The same set-up can be used to dis-
cover whether sugar diffuses throus^h
this membrane. Can you suggest ho\v
this could be discovered?

If conditions are suitable sugar will
diffuse through the membrane until the

123

concentration of sugar is the same on
both sides of the membrane.

Whatever may be true of other mem-
branes and other substances, if you have
done the experiment suggested, you now
know that water and sugar can diffuse
through sausage casing or cellophane
membranes. To test your understanding
of diffusion do Exercise i i.

Diffusion through a living cell mem-
brane. If you place some living plant
cells on each of two slides and add dis-
tilled water (water without minerals) to
one and a very strong salt solution to
the second some interesting results will
be obtained. If you observe the cells
under the microscope, you will find that
those placed in distilled water will swell
slightly. What may have happened to
make them swell? On the other slide
the results will depend somewhat on the
strength of the solution used, but you
will be able to observe a distinct change.
The protoplasm will shrink away from
the wall and form a small mass; evidently
the water vacuole inside the cell disap-
pears. Diffusion of water out of the cell
takes place (see Fig. 153). This is good
evidence that water diffuses through a
living cell membrane. You should now
be able to make some practical applica-
tions of what you have just read in doing
Exercise 12.

When do substances diffuse through
a membrane? To begin with the only
substances that diffuse through mem-
branes in living things are substances
that diffuse or dissolve in water. Not all
substances dissolve in water. If shaken up
in water, they may appear for a time
to do so, but after standing the particles
will fall to the bottom. Such substances

124

Living Things Are Basically Alike unit ii

Fig. 152 Year after year the
pieces of rock are pushed
farther apart by the growth
of the tree. (American mu-
seum OF NATURAL HISTORY)

are said to be insoluble; thev do not dis-
solve. Among many other compounds,
starches and proteins and fats, for ex-
ample, are insoluble in water. Therefore
they do not diffuse through a membrane.
You can convince yourself of this by
doing Exercise 13.

But there are some substances that are
soluble in water and yet fail to pass
through some kinds of membranes. Or
let us state it the other way: some mem-
branes allow certain soluble substances to
pass through but keep out other soluble
substances. The word pcrDieable means
"allowing substances to pass through."
Then we can say that some membranes
are permeable to some soluble substances
and are not permeable or less permeable
to other substances. They are not per-
meable t(; certain very large molecules
or groups of molecules.

Whicli substances enter living cells?
The cell membrane, made up of proto-
plasm, is a good example of a membrane
which differs in its permeability to dif-
ferent substances. Some compounds pass
through; other solui)lc compounds ^ith
molecules of the same size cannot pass
through. And what is more, the cell mem-
brane changes in its permeability. Vari-

ations in light and temperature or the
presence or absence of a great number
of substances make it more or less per-
meable from time to time.

There is much that is not understood
about diffusion of substances into a liv-
ing cell and much that cannot be ex-
plained here. But you must remember
that many, though not all, soluble sub-
stances which come in contact with a
cell enter it. Insoluble substances do not
enter. Starches, fats, and proteins are
insoluble and certainly cannot diffuse
into or out of a cell. But you will learn
later how they are made soluble and how
they enter in their soluble form. Oxygen
is soluble in water and diffuses readily
into a living cell through the membrane.

Thus you can see that as substances
are used up in oxidation in the cell they
are constantly replaced by the substances
that diffuse through the membrane into
the living cell.

Cell activities defined. Now with an
understanding of oxidation in cells and
how the necessary fuel and oxygen enter
them, let us go back and examine again
the activities of a cell.

Food, and certain other necessary as
well as unnecessary materials diffuse into

PROBLEM 2. How Cclls Keep Alive

cells {absorptiov)\ the protoplasm acts
on some of the food, making it usable
(digestion)] the protoplasm makes more
protoplasm from food {assiiiiilation);
some of the food unites chemically with
oxygen, releasing energy which keeps
the cell alive (oxidatioji which is a part
of respiration); some of the energy is
used in movement of the protoplasm
(motio?2); or in moving the whole cell
from place to place {locomotio?i)\ the
protoplasm makes materials useful to it
or to other cells close by {secretion);
waste or unused substances diffuse out
of cells {excretion); as protoplasm grows
a cell may become separated into two
parts, making two new cells in the place
of one old one {reprodiictio?i); the pro-
toplasm is sensitive to its changing sur-
roundings and its activities are frequently
changed when the surroundings change
{irritability)^ Through all these activi-
ties cells remain alive. Taken together
these activities are "life."

The cell theory or cell doctrine. When
Hooke discovered cells in the second
half of the 17th century other men
studied the parts of many different ani-
mals and plants and saw cells of various
kinds. But for almost a hundred years
little was added to the simple idea that
cells could be found in organisms. No
one knew what cells were or how they
were related to the life of the plant or
animal; the importance of the cell was
not understood. About 1820 a French
physician and biologist Dutrochet (Dew'-
tro-shay), published a statement in which
he said that it was clear that all living
things were made of cells and that what-
ever activities a living thing performs
must be performed by its cells. This

y^^V^^"^

Strong salt solution

Fig. 153 The upper cell has been placed in dis'
tilled Vfater, the lower cell in a salt solution.
Why does the cell wall in the upper cell bidge?
Why did the distilled water diffuse inward?
What has happened to the protoplasm of the
lower cell? Why did water diffuse out of it?

important statement which seems so evi-
dent to us was apparently not accepted
at that time. Then in 1838 two German
biologists, Schleiden, who was a botanist,
and Schwann, who was a zoologist,
stated that living things are made up of
cells and that the cells are the important
part of the living thing. Schleiden and
Schwann were so well known that biolo-
gists everywhere began to accept the
cell theory, as it was called, the belief
that all living things are made of cells
and their products. But Schleiden and
Schwann still had not understood the
true structure of the cell. Little was
known about protoplasm; it had not even
been named.

From that time to this, many millions
of plants and animals have been studied
under the microscope and very much
has been added to our knowledge of
cells. Soon after Schleiden and Schwann
made their contributions another botanist

126 Liviiig Things Are Basically Alike unit ii

Hugo von Mohl ( 1 805-1872) applied the these studies have shown the truth of the

name protoplasm (first substance) to the cell theory which states that:

living matter within the cell. Several years i . Plants and animals are made of cells

later an English biologist, Thomas Henry and materials produced by cells.

Huxley (1825-1895), made popular the 2. All the activities of living things are

statement that protoplasm is "the physi- made possible by the activities of cells,
cal basis of life," w hich sums up the idea The evidence for this is now so com-

that wherever there is life there is the plete that we no longer speak of this as

substance protoplasm. Biologists of every the cell theory. These facts have been

country have contributed to our under- so well established that it is better to

standing of the cell and protoplasm. All speak of the cell doctrine.

Questions

1. Which activities distinguish the living from the lifeless?

2. What are some of the activities of the cells of your body?

3. Define oxidation. What kind of substances are formed as the result
of oxidation? Give three examples. Use the words oxidation and
burning in a sentence to show that you understand their meanings.
What, besides oxides, is released in all oxidation? Whei'e in living
things docs oxidation go on? Which substances usually are oxidized in
a cell?

4. What is energy? What two kinds of energy are released in burning?
What is chemical energy and how does it differ from heat and light?
Give examples of changes of one kind of energy into another.

5. What energy change occurs when oxidation takes place in a cell?

6. Give examples of work done by your body; by a plant.

7. What two kinds of substances must enter a cell if oxidation is to
continue at all times? By what process do they enter?

8. Give an example of the diffusion of liquids and explain how they
diffuse. Describe an experiment in which you can see that diffusion is
occurring.

9. Do liquids diffuse through a membrane which has no visible pores?
Describe an experiment which answers this question.

10. Describe an experiment which shows that diffusion occurs through
the living cell membrane.

11. What is the connection between solubility and the abiHt\' to diffuse
through a living membrane? Define the word permeable. What can
you say about the permeability of a living cell membrane? Name
three compounds that do not pass through a cell membrane. What
must happen to them before they can diffuse through a membrane?

12. Name and define ten cell activities.

13. What are the two parts of the cell theory? Give in order the names
and the contrii)utions of the biologists associated with the cell theory.
Why is it better to speak of the cell theory as the cell doctrine?

PROBLEM 2. How Cclls Keep Alive 127

Exercises

1. The behavior of protoplasm. Protoplasm may be seen best in Chaos
chaos or in slime molds. Watch the protoplasm first under low, then under
high power. Do not use a bright light. How does it move? If it continues
to move in one direction note how long it takes to move across the field
of vision. Can you then estimate the speed of motion? Draw out a soft
glass rod to obtain a microneedle. Touch the edge of the protoplasm with
it. What happens?

2. Motion of plant protoplasm. Mount the edge of a young leaf of an
elodea plant on a slide. Warm the slide in your hand. Examine under the
low power. Move the slide about until you see motion in a cell. What is
it that you see moving? Explain their motion.

3. Turn to Exercise 10 on page 69. Make a note of and describe all
the activities shown by the paramecium or other protozoan. If you are
fortunate you may see it dividing into two.

4. What is one striking property of oxygen? Prepare oxygen by heat-
ing a mixture of three parts of potassium chlorate and one part of man-
ganese dioxide. (Consult a chemistry or general science text.) Collect
several small bottles of the gas by displacing water. Into one bottle thrust
a burning splint. Heat some sulfur in a deflagrating spoon until it begins
to burn,'then put it into a bottle of oxygen. Into a third bottle put a strip
of burning magnesium held with forceps. Thrust a glowing stick of char-
coal into a fourth. Describe carefully what you saw in each case. WTiy
does each substance stop burning after a short time?

5. Does the oxygen of the air support burning? Your teacher can
provide you with air from which oxygen has been removed. Thrust a
brightly burning taper into it. What happens? Why? How may your
teacher have removed the oxygen?

6. When does the process of oxidation stop? Fasten a candle to a block
of wood. Float the block in a pan of limewater. Light the candle. Invert
a jar over it so that the mouth of the jar is under the limewater. Why
does the candle go out? What substances are produced by the burning
of a candle? Where do these substances go? Why does the limewater rise?

7. To test your understanding answer the following: (a) How do the
various ways of extinguishing fires take into account the fact that burning
requires oxygen? {b) Can you suggest a chemical explanation of the fact
that substances like carbon dioxide and water do not burn?

8. How can you show that oxidation is going on in your body? Breathe
out for a few minutes through a tube into a small bottle containing a
small amount of clear limewater. What do you note? Explain. Now shake
a similar bottle of limewater so that it is well mixed with the air in the
bottle. Why should this be done? What is the evidence from this experi-
ment that oxidation of a substance containing carbon took place in your
body? Can you think of any other evidence that oxidation takes place in
your body?

128 Living Things Are Basically Alike unit ii

9. Do gases move about? Fill a small bottle with oxygen. Cover with
a glass and stand on a table. Gently place a bottle of the same size, filled
with air, over the mouth of the bottle of oxygen after removing the glass
plate. Seal the mouths together with a strip of adhesive tape. Let stand
for 15 minutes. Remove the upper bottle without disturbing the lower.
At once thrust a glowing splint into the upper bottle. What do you
observe? What is lacking in this experiment? What else should you do?

10. Diffusion of copper sulfate and of red ink. Drop a crystal of copper
sulfate into a tall jar of water and allow the jar to stand without dis-
turbing it. What happens within a day or two? Into the bottom of a
tumbler of water standing quietly on a table carefully place some red ink
with a medicine dropper. Do not stir the water. Record observations.

11. Suppose three billion molecules of pure water are separated by
a membrane from a salt solution containing six billion molecules of water
and two billion molecules of salt. In which direction would the more
rapid diffusion of water through the membrane take place? Why?

12. Remembering that fruits and vegetables are made up of large
numbers of cells with living membranes surrounding them, answer the
following: (a) How can you make sliced peaches juicy for serving?
(b) To freshen lettuce would you recommend fresh water or salt water?

13. Does starch pass through a membrane? Boil some starch in water,
making a "starch paste." Fill the bulb of a thistle tube with this. Cover
with a membrane. Invert in a tumbler of water. Mark the level of the
licjuid in the thistle tube. After the experiment has been standing for
several hours, find out whether starch has passed through the membrane.
How can you do this? Has the liquid risen in the thistle tube? Write your
method, results, and explanations.

Further Activities in Biology

1. Can diffusion be speeded up by changing the concentration of water
in the thistle tube? Fill one tube with thick molasses (since this has much
sugar, the \\ater molecules are not concentrated). Fill another tube with
diluted molasses (there is little sugar so that the water molecules are more
concentrated). Set each in a jar of water. How soon can you see results
of diffusion in each tube? How much rise do you get in each?

2. Set up an experiment to show that several substances can diffuse at
the same time. Use sugar and table salt.

3. Will all kinds of membranes permit water and dissolved substances
to pass through? Set up experiments using membranes of rubber, cello-
phane, oiled silk, and so on. (^nrcfully record your results.

4. Locy's Biology and Its Makers has interesting material on the early
history of the study of cells. Prepare a report. Singer's History of Livifig
Things ma)' be used also, or E. E. Snyder's Biology in the Making.

PROBLEM *J How Are the Cells Arranged in Animals

and Plants?

How animal cells differ from one another.

It has been known for a long time that
the body of an animal consists of cells
and that these cells are not all alike.
Blood cells are very different from skin
cells; muscle cells are different from
either of the other two. Cells vary in
shape or structure, in their position in
the body, and in the work they do. This
is not surprising, ^ut it may surprise
you to learn that cells in corresponding
parts of mice and elephants are much
alike in shape, activities, general appear-
ance, and even in size. You can, as a mat-
ter of fact, learn much about cells in
your own body by studying the corre-
sponding cells in the bodies of cats or
white rats or frogs or other animals. See
Figure 154.

The different kinds of cells are found
in groups. Examination of the arm of man
shows that cells are arranged in groups.
The outside of the arm is made up of
flattened cells called epithelial (ep-e-
thee'lee-al) cells lying together in a
group. Under these are groups of cells
{gland cells) that differ from the flat-
tened cells; substances such as sweat and
oil come from these cells. Still deeper
in the arm are masses of fat cells. All of
these together make up what we call by
the simple name "skin." Under the skin
is \\hat you sometimes call the "flesh."

This is composed of muscle cells in
groups. Among the muscle cells are nerve
cells, blood cells in the blood, and some
other types of cells. At the very inside
of the arm is the bone. The bone con-
tains a huge number of bone cells which
have a very characteristic appearance.
Among the bone cells there are also
nerve cells, blood cells, snd still other
kinds of cells. See Figures 157-159. The
important fact is that the different kinds
of cells are found in groups or masses.
Such a group of cells which are similar
in structure and which do much the
same kind of work in the body is called
a tissue.

Sponge

Fish

Frog

Cat

Cow

Fig. 154 Muscle cells of the sponge, fish, frog,
cat, and cow. Compare these with muscle cells
of man. Figure ifj, page 1^2.

- V

^:i

X ^* ' <►- "^v •V-

■1^ v.. \:-u^ . ■- i-

I ts-- . jifet^.

130 Living Things Are Basically Alike uxn 11

In studying the arm, you just read
about bone tissue, muscle tissue, nerve
tissue, blood tissue, gland tissue, fat tissue,
and epithelial tissue.

Sometimes the cells making up a tissue
deposit some nonliving material around
themselves. This nonliving material is
called intercellular matter. The word
"intercellular" means lying between the
cells. Bone is a particularly good example
of cells that do this. The bone cells sur-
round themselves with a large amount of
mineral matter. This lifeless matter be-
comes an important part of the tissue;
the hardness and rigidity ^\•hich you as-
sociate with bone are due to the inter-
cellular matter. Some other tissues besides
bone have intercellular material, although
the relative amount of intercellular ma-
terial is smaller than in bone. Thus we
nmst add this new idea to our definition
of a tissue and say that a tissue is a group
of cells similar in structure and in work,
along with more or less intercellular ma-
terial which is produced by the cells.

Tissues make up organs. You have read
of a number of tissues found in the arm.
But these same tissues are found in other
parts of the body as well. In general,
each tissue is found in many places
throughout a complex animal like a man
or a cat. And wherever the tissue is found
it is combined with other tissues, making
up a distinct part of the body known as
an organ. An organ is a part of the body
consisting of a group of tissues which
work together. The word organ must
not be mistaken for the word organism
which means a single living tiling or in-
dividual. The luart, the stomach, and
the liver are all internal organs of \-our
body. The skin may be considcrctl an

Fig. 155 A small part of a bone, iiiaii^nijied.
Large dark spots are tubes contaming blood ves-
sels and nerves. S?nall dark spots are spaces
zvhere bone cells used to be. This tissue has in-
tercellular material, (richard st. clair)

organ too, for it also consists of a group
of tissues which work together. You
read that a bone consists largely of bone
tissue but it has also nerve, blood, and
other tissues; it, too, may be considered
an organ. Often an organ does more than
one kind of work, or is useful to the
body in more than one way. P'or example,
the stomach not only helps in digestion
but it helps destroy harmful bacteria;
in it food is temporarily stored and it is
useful to the body in still other ways.

Biologists often use the word function
(funk'shun) to refer to activities or
useful properties of organs, tissues, or
even single cells or parts of cells in an
organism. The stomach functions in di-
gesting certain kinds of food; protecting
other tissues from infection is one func-
tion of the skin; enabling a person to
hear is one function of the ears. To help
you understand this paragraph do Ex-

KRCTSF, I.

PROBLEM 3. How Cells Are Arran^red in Amnials mid Plant

l^^ / ^

^?^L»:

•i

Fig. 156 Which of the organs of this geranium
can you see? Which cannot be seen? (sullivan)

How living things are built up. Thus
you see that organisms, except the very
simplest, are made up of parts called or-
gans; organs are composed of several or
many tissues; tissues are composed of
cells; and all the cells of one tissue are
similar to one another.

Most organisms are so complex that
they have a number of organs working
together in an organ system. For example,
in your body there is the digestive sys-
tem consisting of the various organs
that have to do with digestion. Then
there is the skeletal system which in-
cludes all the bones of the body. You gans as the stomach, the mouth, and other
will read of other organ systems that digestive organs); it includes .yer(9?/^ we?;/-
are composed of a number of organs; braiie (the smooth membrane covering
the organs are composed of a number some internal organs and Hning body
of tissues, and the tissues are composed cavities); and it includes gland tissue,
of cells. You have been reading about Muscle tissue is of three types: volun-
the construction of your body but other tary muscle, involuntary muscle, and
complex animal organisms as well as heart muscle. In Figures 157 and 158 are

S 131

complex plant organisms are also com-
posed of cells, tissues, and organs.

How diflFerences arise in cells. Most
organisms start life as a single cell. This
is true even of the complex animals such
as the vertebrates. This single cell gives
rise to the many millions of cells of
which the organism's body consists. It
is interesting that this cell should be able
to produce types of cells as different
from one another as are the cells of such
tissues as muscle, bone, and nerve tissue.
Many biologists are attemptingr to solve
this problem at the present time. What-
ever the explanation may be, we must
recognize the fact that there is differe?i-
tiation of the cells in an organism. The
cells differ from one another in appear-
ance and in their activities. In the more
complex animals the differentiation is
very marked. Each type of cell can usu-
ally be recognized either by its structure
or by the work it does in the animal or
plant. The cells are specialized in struc-
ture and function.

The main kinds of animal tissues. The
many kinds of tissues in an animal such
as man can be divided into four or five
main tissue groups. Epithelial, muscle,
connective, and nerve tissues are four
groups. The fifth is blood. Epithelial in-
cludes the membrane that covers the
body; it also includes mucous membrane
(the moist membrane that lines such or-

132

Living Tlmigs Are Basically Alike unit ii

Cell body

Nucleus

Intercellular material

illustrations of voluntary and involuntary
muscle. Heart muscle differs from both
voluntary and involuntary muscle in its
appearance and in its activity. Connec-
tive tissue is a large group which includes
tissues of very different kinds. It includes

Fig. 157 (upper left) (A) One type of epithe-
lial cell. HozD 7inp;ht the cilia be used? See also
flat epithelial cells in Fig. 139, page 106. (B) A
single cell of fat tissue. ]Vhat fills the greater
part of the cell? (C) Compare these fibers ii-ith
volimtary ?nuscle fibers. (D) This is a very
simple type of nerve cell.

Fic. [58 (above) Voluntary vniscle fibers. The
dark spots are nuclei of cells. Do you see stripes
running across the fibers? (gknivUAl biolo(;ical

SUl'PLV)

Fk;. 159 (left) Cartilage tissue. Like bone, this
tissue has a large aniount of intcrcelhdar ma-
terial.

bone and cartilage tissues, fat tissue, and
fibrous tissues. By some people blood is
considered to be one type of connective
tissue. Cartila{Te tissue is found covering^
a portion of many bones. It contains no
mineral matter but a large amount of
firm intercellular matter which makes
the cartilage hard, slightly elastic, and
very smooth. See Figure 159. You can

How Cells Are Arranged in Ani?nals and Plants 1 3 3

of an animal so are the tissues. Plants
have no muscle, connective, nerve, or
blood tissues. But they do have tissue
which resembles the epithelial tissue of
animals. It forms a membrane covering
leaves, young roots, and stems and also
forms small amounts of gland tissue. If
you did Exercise 6 in Problem i of this
unit you have seen it. The other tissues
of a plant bear little resemblance to ani-
mal tissues. Many parts of a plant have
groups of thin-walled cells containing
large vacuoles. This tissue is called par-
enchyina (per-en'kim-ma). Parenchyma
cells may or may not have chloroplasts.
Most roots and stems have large amounts
of woody fibers with strong cell walls
and they have ducts of various kinds, as
well as other tissues. Some of these are
shown in Fig. 180, page 155. The tissues
consisting of woody fibers and ducts are
found, too, in the veins of leaves.

Living things are fundamentally alike.
Living things consist of protoplasm. Most
of them consist of many cells. In many-
celled organisms the groups of similar
cells form tissues, and groups of tissues
are organized into organs; the organs
make up the organism. This is true of
both animals and plants.

Fig. 160 Cells ni opion skin.- This tissue some-
ivhat resembles the epithelial tissue of animals.
Which parts of the cell do you recognize?

(RICHARD ST. CLAIR)

get a good idea of several of these tissues
by studying the tissues in a frog as de-
scribed in Exercise 2.

Tissues in higher plants. As in animals,
plant cells are arranged in groups or tis-
sues; and various tissues together make
up the organs, such as the root, the stem,
and the leaf. Just as the organs of a
plant are quite different from the organs

Questions

1. In what ways do cells of an organism differ from each other? Why
is it possible for you to learn much about your own cells by studying
other animals?

2. Define a tissue. Describe a tissue which has intercellular matter. Was
your definition of tissue complete? List the tissues found in a human
arm, beginning with the outside.

3. Define the term "organ." Explain the difference between an organ
and an organism. How is the word "function" used in reference to
cells, tissues, and organs?

4. Name an organ system in the human body.

134 Living Things Are Basically Alike unit it

5. What word do we use to state the fact that cells differ in shape and
activities?

6. What are the four main kinds of tissues in a complex animal? State
which tissues are included in each group. Briefly tell the character-
istics of each type of tissue.

7. Name two important plant tissues.

8. Summarize this short problem in your own words.

Exercises

1. Is a bone a tissue or a collection of tissues? Obtain a beef or lamb
leg bone sawed lengthwise through the middle. Scrape it clean of meat.
Use a strong dissecting needle to detect the covering on the shaft (long
part) of the bone. Describe it. This is a kind of connective tissue. What
might be a function of this covering? Feel the substance, cartilage tissue,
that covers the head of the bone. Describe. Prick the inside of the head
of the bone with the needle. Describe this spongy bone. What makes it
red? This is known as red marrow. Prick the material outside the marrow;
this is true bone tissue. Feel the substance in the inside of the shaft. This
is yellow marrow. How does it differ from red marrow? Examine some
of the red marrow under the microscope. List all the substances vou have
found. Is the bone a single tissue or a collection of tissues? Of course, you
cannot see the bone cells with the unaided eye. Your teacher will give
you a prepared slide of bone tissue. Notice the long dark spots with manv
fine projections. They are arranged in concentric circles (circle within
circle) around a large round opening. In life, blood vessels and nerves
run through these circular openings. Each long spot with radiating pro-
jections is a space in which a bone cell used to lie. The protoplasm has
disappeared.

2. Animal tissues may be studied easily by preparing slides of tissues
from a recently killed frog.

Epithelial Tissue: (a) Squamous (flat). Frogs shed their skin continu-
ously. Place on a slide a bit of shed skin found in the water in which
frogs arc kept. If it tends to roll up be sure to unroll it by holding down
the edges with dissecting needles. Stain with Lugol's solution and cover
with a cover slip. Fxamine and draw the flat epithelial cells. (/;) Ciliated.
Remove a small piece of epithelium from the roof of the mouth of a
freshly killed frog. Make a cut with a scalpel in the region near the
eyeball and with your forceps peel it off. Aloimt the material on a slide,
add a drop of Ringer's solution and a cover slip. Observe the beating of
the cilia.

Muscle Tissue: (a) Voluntary or striated. Cut into the muscle which lies
under the skin on the ventral side of a freshly killed frog. Strip off a
small piece with your forceps. Place on a slide and tease the muscle apart

PROBLEM 3. How Cells Are Arranged in A'tmiials and Plants 135

with two needles. Add a drop of Ringer's solution and a cover slip. Note
the muscle fibers with their light and dark bands. Add a drop of aceto-
carmine stain to one edge of the cover slip and draw it under the cover
trlass by holding a piece of blotter at the opposite edge. Note the many
elon^^ated nuclei within each fiber. Draw what you see. (^) liivohnitary
or smooth. With your scissors remove a small piece of the stomach of
the frog. On this piece separate the inner coat from the outer coat with
your needles. Lay the outer coat on a slide and tease apart the cells
of the thick outer coat of muscle. Stain with aceto-carmine and add a
cover slip. Observe the long thin cells, packed closely together. Do you
see the long nuclei? How do these cells difi^er from the voluntary muscle
fibers? Draw.

Blood Tissue: Place a drop of blood on your slide and add a cover slip.
What shape are the red blood cells? Do they have nuclei? Draw.

Further Activities in Biology

1. A viseful project is the preparation of models of different kinds of
tissue cells. These models can show the shape, relative size, and special
characteristics of the cells.

2. By using a magnifying glass and a scalpel, try to learn something
about plant tissues. Can you distinguish difi'erent tissues in a young stem?
Examine a thick leaf for tissues. Describe what you see. If you have a
microscope you may be able to see some of the cells after teasing some
of the tissues farther apart.

/// UNIT III yon will consider these problems:

Problem i . What Part Do Leaves Play in Making and LTsing Food?
Problem 2. What Part Do Roots and Stems Play in ALiking and
Using Food?

UNIT III GREEN PLANTS MAKE THE FOOD USED

BY ALL LIVING THINGS

Fk;. i6i a ivbciit field at harvest tlvie. Wheat is the basic food for many vnlHons of
people, lor Diillions of others the basic food is rice or rye or barley or potatoes. We
do not eat the green parts of any of these plants, but the parts that we do eat can
develop only on green plains. Do you know why?

PROBLEM 1 What Part Do Leaves Play in Making

and Using Foods?

An interesting experiment. Starch, sugar,
protein, and fat are all found in plant
protoplasm. You learned this in the last
unit. Do they get there from the soil?
Are thev made in the plant from soil
materials? Just where do they come
from? This question of how these com-
pounds get into a plant and how a plant
grows has interested people for a long
time. Early in the 17th century Jan van
Helmont, a Flemish physician, performed
a simple experiment which helped a little
toward the answer. He weighed the soil
in a large tub and planted a small willow
branch in it. For five years he watched
it carefully and watered it regularly with
rain water. At the end of this time the
branch had grown into a small tree
weighins^ more than 160 pounds. Then
he weighed the soil once more. He was
amazed to discover that the soil weighed
only two ounces less than when he
started the experiment! The experiment
was convincing proof that the soil was
not the source of the bulk of the mate-
rials used in the growth of the willow
tree. Evidently the soil supplied only the
tiniest part of the materials used by the
willow in its growth. To discover where
the rest came from we must study the
plant. Let us begin with the leaves.

Differences in leaves. Some kinds of
plants, like the Spanish moss and some
kinds of cactuses, have little or nothing

by way of leaves. The cone-bearing trees,
such as the pines, spruces, hemlocks, and
others have needlelike leaves. But in gen-
eral the green plants have broad, con-
spicuous leaves. Leaves vary considerably
in size and shape. In the everglades of
Florida there grows a fern, the one from
which the Boston fern was developed,
with a leaf long enough to stretch the
length of a large-sized room, 20 feet.
One species of pine has needles 1 2 inches
long, while the needles of cedar may be
less than a quarter of an inch long.

Parts of a leaf. Many leaves have two
distinct parts: a stemlike part called the
petiole and a flat, wider part called the
blade. There is great variation in leaf
blades. They may be narrow and pointed
as in the grasses or the common iris; they
may be almost round or shield-shaped
as in the water lily. They may be smooth
or hairy, paper thin or relati\ely thick
and stiff. Leaves vary in color, too. When
the poinsettia bears its small, inconspic-
uous, yellow flowers the upper leaves
are not green but bright scarlet. The
leaves of the purple beech throughout
its whole existence do not appear green.

Leaves also differ in veining. You read
in Unit 1 that leaves may be parallel
veined (as in the monocotyledons) or
net veined (as in the dicotyledons). And
net veining may be of two types as shown
in Figures 1 14-1 17, page 85.

138

All Food Is Made by Green Plants unit hi

Close study of the leaf blade. Althouijh
the \ariation in leaf shape and size is
interesting, we can learn very little about
the activities of a leaf from this kind of
study. To learn more it is necessary to
study the internal structure. This can be
done by examining a thick fleshy leaf
from a plant such as sedum. We can
break or cut the leaf crosswise and, with
the aid of a knife, pull off^ some of the
"skin." When we hold this to the light,
we discover that it is thin and trans-
parent. This "skin" is found on both the
lower and upper sides of leaves. It is a
tissue called the epidermis (ep-i-der'mis).
You will notice that the exposed part
under the epidermis feels moist and soft.

If \'ou use a microscope to examine a
thin slice made across an ordinary leaf
you will have no trouble in identifying
the parts of the leaf. You can see the
upper and lower cpidciyf/is, the spongy

Fig. 163 (above) Water lily. The leaf blade
floats on the water. Its long petiole is attached
to a stem at the bottom of the pond, (new york

BOTANICAL GARDEN)

Fig. 162 (left) Spanish vioss hafiging on live oak
branches. It is not a moss but a flowering plant.

(NORTH CAROLINA DEPARTMENT OF CONSERVATION
AND development)

cells with air spaces between them, the
palisade cells, and the veins. See Figure
164. You can easily study the epidermis
by doing Exercise i . Study of many dif-
ferent leaves will be interesting.

Leaf epidermis. Every leaf, thin as it
may be, is covered above and below with
epidermis. This tissue consists of cells
closely fitted tooether. Fitrure 16c is a
drawing of lower epidermis of a sedum
leaf. In addition to the ordinary trans-
parent and usuall\' colorless cells, there
are at frequent intervals pairs of green
cells, each shaped like a slender kidney
bean. These cells lie in such a way that
there is an opening left between them.
This opening is called a stoma (stoh-ma).
Each stoma connects an air space within
the leaf with the air outside. The upper
epidermis of most plants has few or no
stomata (stoh'ma-ta), plural of stoma;
its cells, then, are mostly all alike.

PROBLEM I.

Upper surface of leaf

Spongy

cells

The Part Leaves Play in Making Food

Upper epidermis

139

Side view of stoma

ein fconducf-
ing cells of leaf)

Lower epidermis
Chlorophyll bodies

Fig. 164 Lookhjg into a leaf. Which two layers
lie between upper and lower epideriuis? What
is in the "empty" spaces between the spongy
cells?

In most plants the two cells enclosing
the stoma, called guard cells, ordinarily
take the shape of a half doughnut during
the daytime, making the opening larger.
At night they straighten out, making the
stoma smaller. The opening is never shut
completely. The stomata are extremely
numerous. A medium-sized cabbage leaf
probably has about 1 1 ,000,000 stomata,
and a sunflower leaf may have up to
about 1 3,000,000. In most land plants the
stomata are more numerous on the lower
side; in floating leaves they are more
numerous on the upper side; none occur
on leaves that grow submerged in water.
To determine the number of stomata, do
Exercise 2.

What makes the leaf green? As you
study a fresh section of a leaf under the
microscope, what strikes you most is
the bright green color, particularly of
the palisade cells. There is usually less
green color in the spongy cells and the
epidermis has faint traces of green in the
guard cells only. This color is caused by
the presence of the tiny green bodies

Stoma Guard cell Epidermal cell

Fig. 165 A tiny piece of lower epidermis. How
many stomata do yon see? Are they open or
closed? What are the cells on each side of a
sterna called?

within the cytoplasm, the chloroplasts.
They are often oval in shape. They are
made of protoplasm containing several
coloring matters, one of which is bright
green in color. This is the chlorophyll.
Chloroplasts are found not only in leaf
cells but in all parts of the plant which
look green. Fruits are green before they
ripen and stems always have chlorophyll
when they are young; sometimes they
keep their green color throughout the
life of the plant. You probably saw
chloroplasts in Elodea cells when study-
ing the preceding unit.

(Optional) Chloroplasts, In most green
cells the chloroplasts are small globular
bodies as indicated in Figure 164, but in
some cells they are large and of unusual
shapes. In the alga Spirogyra, the chloro-
plasts are spiral bands. There may be one
or several in each cell. In certain other
algae the chloroplasts are star shaped.
But a chloroplast is always a living struc-
ture which under certain conditions be-
comes very active. The chlorophyll
itself is a mixture of two compounds.

140

All Food Is Made by Green Plants unit hi

Fig. 166 Miles of green plants -a-ith tl:eir chloroplasts zvorkhig actively. Wl.iat are the
results of their work? How does the work of the chloroplasts benefit the plants? How
does it change the atmosphere around them? (department of conservation, Michigan)

each made up of the elements carbon,
hydrogen, oxygen, nitrogen, and mag-
nesium. The only way you can obtain it
in the laboratory is to extract it from the
chloroplasts by means of alcohol. To-
gether with the chlorophyll, but hidden
by it, are yellow substances; one of these
is carotene, a substance very important
to you (see p. 178). It may be present in
the chloroplast in large amounts. It shows
clearly in carrots, apricots, sweet pota-
toes, and yellow corn where there is no
chlorophyll present to hide it.

Usually chlorophyll forms only in the
presence of light although the yellow
substances may be made either in light
or dark. If a plant sprouts in the dark it
will not be green. On the other hand,
strong light causes the chlorophyll to
decompose or disappear, and a leaf ex-
posed to strong light is green only be-
cause its cells are acti\'e and new chloro-

phyll is constantly being formed. In the
fall, as the weather becomes cooler, the
leaves form chlorophyll at a slower rate.
It is then that the yellow coloring, which
has been hidden by the green, shows up,
giving the brilliant yellow tints to some
autumn foliage. In some leaves, as less
chlorophyll forms a new red coloring
appears.

The work of chloroplasts. A vast
amount of work may be done within a
green leaf. Do Exercise 3 to learn that
green leaves make starch in the pres-
ence of light. In the presence of light
each chloroplast is working actively. It
is combining two simple compounds;
water (H.O), which has risen to the
leaf from the roots, and carbon dioxide
(CO^,) which has entered the leaves
from the air through the stomata. And
what is the result of this combining, or
synthesis as chemists commonly call it?

PROBLEM I . The Part Leaves Flay in Making Food

141

Honey

Grape

Double Sugars (C12 H22 On

Pofafoes

Single Sugars (C6 Hi 2 Od) Starches (C6 Hio O5) KZM'

Fig. 167 Did you believe that sugars and starches were rnade in factories? They are
made in plants. All we do is take them out of the plant, and theti refi?ie and pack them
in the factory. Which plants supply starches? Which supply sugars.''

It is a compound consisting of the three
elements carbon, oxygen, and hydrogen.
It is a sweet compound known as grape
sugar (CgHioOe). In most plants this
grape sugar is quickly turned to starch
(CgHioOg)!!. Both sugar and starch be-
long to a class of compounds called car-
bohydrates as you may recall (see page
no). You can show that the plant needs
chloroplasts to make sugar by perform-
ing Exercise 4.

The process of sugar synthesis in leaves
was studied for many years before it
was understood. The process is still not
clearly understood, and only very re-
cently have chemists learned to imitate
imperfectly in the laboratory what plants
have always done within their green
leaves. Even now chemists can produce
only tiny amounts of sugar and starch.
Study Figure 1 67 to see where we obtain
most of our carbohydrates.

142

All Food

Fig. 168 Plants ?nake protein as well as carbo-
hydrates and fats. How do they obtain the
necessary nitrogen, sulfur, and phosphorus?

A busy factory. In a factory electrical
energy may be changed into mechanical
energy, or perhaps chemical energy may
be changed into mechanical energy.
Work is done. In the living leaf the hum
of machinery cannot be heard, the work
cannot be watched by the human eye.
Yet sugar is being made and energy
changes are taking place. It has been es-
timated that the leaves of a single corn
plant within a season make about two
pounds of sugar; the leaves of a medium-
sized apple tree may make 44 pounds
of sugar.

This work goes on in the daytime,
while light strikes the plant. Light en-
ergy from the sun, or radiant energy as

Is Made by Green Plants unit hi

it may be called, is absorbed by the
chlorophyll. In the manufacture of sugar
this light energy is changed into chem-
ical energy, which remains locked up in
the food. All day long while the sun is
beating on the broad surface of the leaf
blade the chloroplasts within absorb the
rays of light. Even on gray days when
there is no direct sunlight, chloroplasts
absorb light energy and continue the
synthesis (making) of sugar, though
more slowly than in bright light. At night
the process stops. Devise and perform
an experiment to convince yourself that
light is necessary for making carbohy-
drates. Electric lamps may be used as
the source of light.

Because light energy is used in the
synthesis of sugar the process is called
photosynthesis. Photo is the Greek word
for light. When carbon dioxide and wa-
ter are combined during photosynthesis,
free oxygen is left over. You can demon-
strate this by doing Exercise 5.

Protein synthesis. Some of the sugar
made by the plant is built up into pro-
teins. You will remember that protein
contains more elements than sugar. Be-
sides carbon, hydrogen, and oxygen, it
contains nitrogen, sulfur, sometimes phos-
phorus, and others. These elements enter
the plant from the soil in the form of
mineral compounds. It is interesting to
note that a plant uses only simple com-
pounds, never elements, in making its
food. Small amounts of these minerals
combine with the sugar. The union does
not take place all in one step; compounds
simpler than proteins are made first.
Among these compounds are amino
acids. You will read more about amino
acids when you study digestion.

PROBLEM I . The Part Leaves Flay

The chlorophyll takes no part in the
synthesis of proteins. In fact, protein
synthesis takes place in all other parts of
the plant as well as in the leaves. It oc-
curs in practically all plants, whether
green or not green. Yet animal cells, as
far as we can tell, never make proteins
from sugar and simple mineral com-
pounds.

Proteins are important for the plant.
As you have learned in the last unit pro-
tein is one of the compounds which is
used in making protoplasm. And without
the making of protoplasm there can be
no growth.

Fat synthesis. Some of the sugar is
changed into fats. Fats, like carbohy-
drates, are made up of carbon, hydrogen,
and oxygen. Some of the oxygen is lost
from the sugar in the making of fats, so
fats have proportionately less oxygen
than carbohydrates. This process, too,
does not depend on chlorophyll; it can
go on in any part of the plant. In some
plants much fat forms and accumulates,
often in the fruit and seed. The kernel
of corn, the fruit of the olive tree, and
the seed of the cotton plant among many
other seeds and fruits contain large
amounts of fat (oil).

Another use for sugar. In most plants,
when a certain amount of sugar has ac-
cumulated, it is changed into starch. The
starch grains in a cell are easy to recog-
nize. See Figure 169. This starch may
soon be changed back again to sugar or
it may accumulate in the plant. The
sugars which are not built up into fats
or proteins have another important use
in the plant. They are oxidized in the cell.
Fats and proteins may be oxidized too,
but generally it is sugar.

in Making Food

143

Fig. 169 Cells of the potato containing starch
grains. From what is starch made in a potato?

In oxidation energy is released. Some
of the energy released by oxidation of
sugar is used in making fats and proteins.
Other small amounts are used in assimila-
tion, the process of making protoplasm
from food. Some of the energy is lost
from the cells as heat. All this energy
comes from the oxidation of sugar in the
cells in every part of the plant.

Respiration in plants. Oxidation is the
union of oxygen with a substance. Ox-
idation in the plant is called respiration.
If the substance oxidized is sugar, two
simple compounds result: carbon dioxide
and water as indicated in the following
equation.

carbon dioxide + water
6CO2 + 6H„0

Respiration goes on in all the living cells
all the time. As a result of photosynthesis
in the green parts in the daytime, there
is a steady production of oxygen in the
cells. Some of this stays in the plant and
combines with food in oxidation. But
so much is produced that it is easy to
demonstrate oxygen passing out of green

Sugar -[- oxygen

144

All Food

leaves in bright sunlight. At night photo-
synthesis stops. Then the concentration
of oxygen inside becomes less than out-
side, and, consequently, oxygen dif-
fuses from the surrounding atmosphere
through the stomata into the leaves and
into the cells.

Now in respiration carbon dioxide is
made. In the daytime it stays inside and
at once combines with water in the
process of photosynthesis. But at night
the carbon dioxide produced in respira-
tion is not used up by the cells and car-
bon dioxide passes out of the cells. Note:
Though respiration goes on all the time,
it is only at night that oxygen enters the
plant and carbon dioxide leaves.

Now in animals much oxygen con-
stantly enters the animal, and much car-
bon dioxide is given off. The breathing in
of oxygen is followed by oxidation of
food all through the animal's body. In
animals, cellular respiration is the term
applied to the movement of oxygen into
a cell, the oxidation of food, and the
passage of carbon dioxide from the cell.
In plants there are no breathing organs
and there is no active breathing, but it
is important to remember that there is
respiration and that when oxygen is not
already present in the plant it diffuses
inward, and that when the carbon diox-
ide is not used in makinjj su^ar, it dif-
fuses outward.

Respiration and photosynthesis. The
exchange of gases that results from respi-
ration and photosynthesis must not be
confused with the processes themselves.
The two processes are altogether dif-
ferent. See the table on page 145.

What part do leaves play? ^()u liavc
seen that leaves play a very important

Is Made by Green Pkfits unit hi

part in the life of the plant. The cells
in the inside of the blade of the leaf con-
tain chloroplasts. Chloroplasts are tiny
bodies of living matter containing chloro-
phyll. Through the agency of the chlo-
rophyll, sugar is made. The sugar can
change to starch. It can also combine
with mineral compounds, making pro-
teins. Sugar is also converted into fats.
These later changes can take place in
other parts of the plant as well as in the
leaves. But photosynthesis takes place
only in the green parts of the plant; this
means that in most plants the manu-
facture of most of the carbohydrates oc-
curs in the leaves. Photosynthesis takes
place only in the stems of such plants as
the barrel cactus (Fig. 186, p. 160). Its
tiny leaves soon drop off.

The manufactured protein is combined
with other substances and changed into
living protoplasm by assimilation. The
carbohydrates, and to some extent the
fats and proteins, are oxidized in respi-
ration. It is by this process that the plant
gets the energy needed for its activities.

How green plants are of importance in
the world. You have seen that green plants
make their own food. But they do far
more than this. They make the food used
by the whole world of animals and non-
green plants. Carbohydrates are made
only by plants containing chlorophyll;
proteins are made only by plants. Ani-
mals and nongreen plants are completely
dependent on green plants for their food,
and that means for their energy supply,
too. Green plants transform the radiant
energy of sunlighr into the chemical
energy in food. Without chlorophyll this
energy transformation could not have
taken place. Green plants keep storing

PROBLEM I . The Fart Leaves Play

energy. Animals and the colorless plants
use up the stored energy in growing and
keeping alive.

Lastly green plants, besides making
foods containing energy, put free oxygen
into the air. In photosynthesis much oxy-
gen is set free. To be sure some remains

m Making Food 145

in the plant and is used in oxidation but
large amounts are left over. This extra
oxygen diffuses into the air. Thus animals
and colorless plants are dependent on
green plants for food, for all their energ\
supply, and for the continued supply of
oxygen. Now try Exercise 6.

PHOTOSYNTHESIS

RESPIRATION

Materials Used
Materials Produced
Energy Changes

When Occurring
Where Occurring

Carbon dioxide and water

Sugar and oxygen

Light energy changed to
chemical energy of sugar

Only in light
Only in green cells

Food and oxygen

Carbon dioxide and water

Chemical energy of food
changed to other kinds of
energy

At all times

In all living cells

Questions

1. What evidence have you that green plants do not get their food from
the soil?

2. How do leaves vary in shape and size? Describe the veining in the
blade of a monocot and in the blade of a dicot. Sketch three leaves to
illustrate "feather" veining, "palmate" veining, and parallel veining.

3. What in a leaf blade occupies the place of the two slices of bread
in a sandwich? What in the leaf takes the place of the sandwich fill-
ing? Locate spongy cells, palisade cells, veins.

4. Describe stomata, giving their appearance and location.

5. Distinguish between chlorophyll and chloroplast.

6. What elements are found in chlorophyll? How can you ^et the
chlorophyll out of a leaf? Explain the effects of light on chlorophyll.

7. Explain what useful work chloroplasts do. To what extent can man
duplicate this work?

8. Give one example of an energy change in a factory and another in
a green leaf. What simple compounds are combined in making sugar?
What substance is left over in this process? What does the word
"photosynthesis" mean?

9. What elements are contained in sugar? in protein? What is combined
with sugar when protein is made? When sugar is synthesized into
protein what simpler substances are produced first? What use does
the plant make of protein?

10. Name three plants which contain large amounts of fat. From what
is fat made in the green plant?

146 All Food Is Made by Green Plants unit hi

1 1 . What use is made of carbohydrates besides conversion into other
food compounds? Of what importance is oxidation to the plant?

12. Define respiration. Where in the plant does it occur? What gas is
used up in respiration? What gas is produced? Explain \\ hv carbon
dioxide diffuses out of a green plant at night but oxygen diffuses out
in the daytime.

13. To sum up, contrast respiration and photosynthesis as to gases used in
each process; gases produced in each; energy transformation in each.

14. Review the work done for the plant by the leaf, showing that chloro-
phyll is essential for making foods and for obtaining energy.

15. iMake the following applications of your knowledge: (a) What do
you recommend for taking out grass stains? (b) Why may leaf-eating
insects kill a tree? (c) How must celery plants be treated to make
them white?

16. Why are green plants of such great importance to you?

Exercises

1. What is the structure of the epidermis of a leaf? Narcissus, trad-
escantia, or many other leaves may be used. With a scalpel and a pair of
forceps remove a bit of the epidermis from the lower surface. Mount in
a drop of water. Examine it under low power. Do you see the tiny open-
ings or stomata? Study the cells that enclose them. How do these cells
differ in shape from the other cells of the epidermis? How many of these
cells enclose a single stoma? What are they called? Are the stomata
always the same size? Explain. Draw a portion of the epidermis showing
all of the structures that were mentioned. Label.

2. Are there more stomata in the upper or lower epidermis? Remove
small pieces of epidermis from the lower and upper surfaces of a leaf.
Examine each under low power. What differences do yo" note? Count
the stomata in the field of vision. How could you arrive at an estimate
of the number of stomata on each surface of the leaf?

3. Do green plants make starch in the presence of light? Keep a gera-
nium or coleus plant in the dark for about one week. Then cover one leaf
with carbon paper, and set the plant in strong light for four or five hours.
Test the covered leaf and an uncovered leaf for starch. (Hint: boil the
leaves in water and extract the chlorophyll with hot alcohol; then test them
for starch by adding a weak iodine solution.) What do you find? How can
you explain it?

4. How can you prove that the presence of chlorophyll is necessary
for carbohydrate synthesis? Eor this experiment you will need plants
with leaves partly green and partly white, such as green and wiiitc coleus,
silver leaf geranium, or variegated tradescantia. Place the plant in the sun-
light for several hours. Remove one or two leaves and test them for starch.
You must be sure to dissolve out the chlorophyll first. Docs this experi-
ment have a control? Would it be as good to use a leaf that is completely

PROBLEM I. The Part Leaves Play in Maki?ig Food i^j

white? Explain. (Note: You use the starch test because it is easy to test
for starch in a leaf. The plant makes sugar first and later changes it to
starch).

5. Demonstration by the teacher. The release of oxygen by a green
plant can be demonstrated if advantage is taken of the fuming of white
phosphorus (DANGER) in the presence of oxygen. (The reaction forms
phosphorus pentoxide.) A piece of white phosphorus is fastened to a
cork which is then used to close one end of a large tube about one inch
in diameter. Water is poured into the tube, leaving an air space of three
or four inches. Elodea plants are introduced and the tube then closed
bv means of a second cork at the other end. When the tube is inverted
so that the phosphorus is in the air space, fuming occurs. After a time
all the oxygen will have been removed from the air. The glass tube is
then turned so that the phosphorus is in water. After having been kept in
the bright sunlight the tube is inverted again. Fuming occurs a second
time showing that the elodea plant must have released oxygen. The dem-
onstration may be repeated several times.

6. Read again the account of Van Helmont's experiment with the
willow twig, page 137. Van Helmont concluded that the plant made its
substance from water. This was a reasonable conclusion considering the
knowledge available to him. List the facts you know that make Van Hel-
mont's conclusion unacceptable today.

Further Activities in Biology

1. What is the effect of a constant electric light upon the leaves of a
plant? Start some bean seedlings in moist sawdust, then transplant to
soil. Use plants of the same size. When the cotyledons have shriveled
place half of the plants under a strong electric light at night. Keep all
of the plants in the light (sunlight, if possible) during the day. Compare
the leaves in the two groups of plants. Has the electric light made any
measurable difference? Try the starch test on leaves from each of the
two groups of plants. What do you find? Explain.

2. Can you detect any difference between the gases that diffuse from a
plant not engaged in photosynthesis and one in which photosynthesis is
going on? Devise an experiment to demonstrate this.

3. Devise an experiment to show what effect darkness has on chloro-
phyll formation in growing plants.

PROBLEM A What Fart Do Roots and Stems Play in

Making and Using Food?

The plant underground. If we were
buried up to our waists, an observer
would get a false impression of us. But
that is the way you see most plants. Half
of the organism or more perhaps, is be-
neath the ground; the roots often spread
out as far as the stem with its branches.
The farther out or down the roots ex-
tend, the better they anchor the plant
in a storm and the more water they can
obtain. If you have growing bean plants,
uproot one and do Exercise i.

Some plants have one long main root
corresponding to the main trunk of a
tree; this is called a taproot. (See Fig.
170.) The taproot may grow to a length
of twenty feet. It is more common for
plants to have many medium-sized roots
joined to the stem just below the surface
of the ground and branching in all
directions (Fig. 172). Just as a stem
branches into finer and finer twigs so
roots divide and subdivide into smaller
roots and rootlets. The finer rootlets
may be so small that one can scarcely
see them; the smallest twigs are thick
in comparison. The root systems of some
plants are astonishingly large. One biolo-
gist estimated that the total length of
the roots and rootlets of one rye plant
was two million feet; yet the plant was
only two feet high.

Sometimes roots are thick and fleshy
and contain large amounts of sugar and

starch. Man uses such roots as the car-
rot, sugar beet, turnip and sweet potato
as food. However, not every fleshy un-
derground part is a root. The Irish po-
tato and the onion, for example, are
stems, not roots.

Roots above ground. Just as stems in
certain plants may be underground, so
may roots grow above ground. English
ivy, Boston ivy, and poison ivy have tiny
roots all along their climbing stems.
These roots cling to a stone or the bark
of a tree and support the plant. In the
jungle where the air is always moist
many kinds of orchid plants are perched
on the limbs of trees. They have roots
which hang down but never reach the
ground.

Soil. You can learn a great deal about
soil at first hand by doing Exercises 2,
3, and 4. There are many different kinds
of soil. The soil of the forest floor is very
diff"erent from the soil at the edge of the
sandy beach. The black loam of Iowa
difl^ers from the red clay of New Mexico.
The soil in your back yard may not be
like any of them. But soil always contains
among other things small particles of
mineral compounds. Sometimes these are
very tiny, as in clay; sometimes they are
large, as in sandy soils. These mineral
compounds are nitrates, sulfates, phos-
phates, and man\' other compounds; no
two samples of soil taken from different

PROBLEM 2. The Part Stems and Roots Play in Making Food

149

Fig. 171 (above) The sugar beet has a much
thickened taproot. Can you calculate through
how many cubic feet of soil these roots spread?

Fig. 170 (above) Yozi can use the yardstick to
tell how far this taproot extends underground.
How high is the ste?)!? (Illinois agricultural

EXPERIMENT STATION)

Fig. 172 (right) The wheat plant has fibrous
roots. How do they differ from the roots of the
sugar beet? How far down do they extend?

I50

All Food Is Made by Green Plains unit hi

Epidermal cell with beginning
of root hair

Soil particles clinging
to root hairs

regions would have exactly the same
composition of mineral substances.

Ordinary soil contains much besides
minerals. It has varying amounts of dead
and partially decayed plants and animals.
The soil from the forest floor, called
humus, is particularly rich in this. And
all soil contains water; even soil that looks
and feels dry contains small amounts of
moisture. This soil water holds in solu-
tion whatever substances in the soil are
soluble. It is quite different from rain
water. Finally, soil contains varying
amounts of air. The nearer the surface
and the less closely packed, the more air
it contains.

A close-up of roots. When you uproot
a plant it is impossible to see one very
important part of the root system, the
part that is most active. This part can
be seen only if the young roots grow in
water or on a moist surface under glass.
See Exercise 5. You will find that near
the end of each little root there is a deli-
cate fuzzy covering consisting of tiny
hairs, called root hairs. See Figure 173.
It is difficult to conceive of the large

Root hair

Fig. 174 (above) Three root hairs ifjagnified
Each hair is a single cell.

Fig. 173 (left) Sprojiti/ig seeds. Each one has a
young root with root hairs. Where on each root
are the shortest root hairs? (blakiston)

number of root hairs on one plant even
though only a part of each rootlet is
covered with them. On the rye plant re-
ferred to above there might be, accord-
ing to some estimates, 14 billion root
hairs with a total length of 6000 miles.

Each root hair is an outgrowth from
and therefore a part of a single epidermal
cell. Like many other plant cells it has
only a thin layer of cytoplasm lining the
cell wall; the interior is completely oc-
cupied by a large vacuole. Figure 174
is a drawing of some of the epidermal
cells of a young root.

Diffusion through root hair membranes.
In the last unit you read how the mole-
cules of all substances are in constant
motion, and how substances, especially
gases and liquids, intermingle or diffuse.
You learned that many substances diffuse
throu[rh a membrane which has no vis-
ible pores. You showed that water can
diffuse through the cell membrane of
plant cells, passing both in and out.

Now let us consider what happens in
the root hair stretched out in the soil
and surrounded by soil water. Does the

PROBLEM 2. The Part Stems and Roots Play in Making Food

soil water enter the cell? First let us con-
sider the water itself; later we can con-
sider the dissolved salts (mineral matter).
In diffusion the movement of each sub-
stance is independent of the movement
of every other. The root hair is com-
pletely surrounded by a membrane. The
vacuole within the root hair contains
cell sap which is a solution of various
substances in water. Because of the many
compounds dissolved in the cell sap the
concentration of water is relatively low.
The soil water on the other side of the
membrane is normally a weak solution
of minerals; it has few minerals and a
relatively large percentage of water. In
other words, the weak solution has a
crreater concentration of water molecules;
it may be 97 per cent water as compared
to 80 per cent water making up the cell
sap. As a result, water will pass into the
root hair.

If the soil water happens to be a very
concentrated solution (have a large per
cent of mineral matter and a compar- leaving the water concentration about

151

able to pass through the membrane. The
protoplasm lining the cell wall is perme-
able to them. Each mineral passes inde-
pendently of the others. When a mineral
in the soil water is present in higher con-
centration outside than in the cell sap,
it passes from the soil into the root hair.
But the movements of minerals are not
always simple; electrical charges and
other factors play an important part.
There is much about their movement
that cannot be explained here and also
much that is not understood.

What happens to the compounds once
they are in? As more and more water en-
ters the root hair, you would expect the
cell sap to become a weaker and weaker
solution. The water concentration in-
side, therefore, would gradually become
greater and would soon equal the con-
centration of the water outside. But this
does not happen because the water that
enters does not remain in the root hair
cell. It diffuses to a neighboring cell

ativeh' low per cent of water), water
will diffuse out of the cell; the plant
would lose water through its roots and
dry up in consequence. Diffusion of
water from the plant takes place when
large amounts of salt are sprinkled on the
ground. This is sometimes done to kill
unwanted plants but it should not be
done if the same soil is to be used for
other plants. Under normal conditions,
however, water does not diffuse from the
root to the soil; it goes from soil to root.
We are now ready for the second
question. How do the nitrates, sulfates,
phosphates, and other mineral com-
pounds enter the root hair? They are
dissolved in the water of the soil and are

as it was before diffusion began. Thus
water keeps diffusing into the plant.

The same is true of some mineral sub-
stances; they do not become concen-
trated in the root hair. They pass right
on to the next cell toward the interior
of the root. In this way, both water and
minerals pass inward from cell to cell.

What is the structure of a root? By
making sections through a carrot, as de-
scribed in Exercise 6, you can learn the
general structure of a root. In almost
all young roots the tissues are arranged
in three distinct cylinders. The outer-
most cylinder of one layer of cells is the
epidermis; inside of this lies the cortex,
several to many cells in thickness; in the

152

All Food Is Made by Green Flams unit hi

Epidermis
Cortex

xylem

cambium

phloem

Growing point
Root cap

Fig. 175 The tip of a root. Note the position of

the xylan, the phloe?n, the caiiibimn, the cortex,
the epidermis, and the root cap.

center is the conducting or vascular cyl-
inder. In the carrot the cortex is relatively
thicker than in most roots; most of the
food accumulates there.

The cortex originally consists of thin-
walled, closely packed, more or less
rounded cells. Later there may develop
in it various thicker-walled cells which
give strength to the root. Also, cork tis-
sues form just beneath the epidermis.
The outer cork cells die, cutting off the
epidermis from contact with other living
cells of the root, killing it. Most cork
tissues are quite impermeable to water,
so water can enter only the youne^er
portions of roots in which the cork has
not yet formed. The young portion of
roots is near the tip where the root grows
in length. This is where the root hairs
form.

Fig. 176 In cutting across a yoimg root one can
recognize three cylinders. IS! ame them in order
begijming on the outside. In very young roots
the xyle?fi cylinder is fluted.

The vascular cylinder has various
kinds of cells. Near its center, in most
cases, there are water-conducting tubes.
These tubes form from cells that lie end
to end through the length of the root.
The cross walls that originally separated
each cell from those above and below it
disappear in time. Spiral thickenings
form lengthwise in the walls, and then
the protoplasm within disappears. Thus
long, thick-walled tubes are built up.
(See C in Fig. 180, page 155.) These
tubes vary in length from a few inches
to several yards, depending on how
many cells have joined together. Exer-
cise 7 may help you remember the vas-
cular cylinder.

Among the tubes usually lie ivood
fibers. Each fiber is a long slender cell
which loses its protoplasm; its w^alls
chantTc into an elastic, tough, woody
material. The fibers give great strength
to the root. These fibers, together with
the tubes, are spoken of as xylem (zye'-
lem) the Crock Mord for wood. The
xylem makes up the inner portion of the
vascular cylinder.

PROBLEM 2.

The Part Stems ajtd Roots Play in Making Food

153

x'Vlong the outer portion of the vas-
cular cyhnder lie tissues known as phloevi
(flow'-em). In the phloem are several
kinds of cells; those of special interest
are the sieve tubes. A sieve tube is a row
of long narrow cells which remain alive.
In this respect sieve tubes are different
from the xylem tubes. Holes appear in
the walls at the top and bottom of each
cell so that these walls look like sieves.
Strands of cytoplasm pass through the
sieve from cell to cell.

Between the phloem and xylem lies
a very narrow ring of thin-walled cells,
the cambiimi cells, which also remain
alive. They, unlike the phloem or the
xylem, have the ability to divide. The
cambium ring is so narrow that it can-
not be seen without the aid of a micro-
scope.

What is the structure of stems? All
roots are very much alike in their gen-
eral structure but there are two distinctly
different kinds of stems. The monocot
stems are quite different from the dicot
stems. First let us study the stem of a
dicot shrub or tree. How does this stem
compare with the root? It has the same
cylinders as the root with which it con-
nects: the epidermis, the cortex, and the
vascular cylinder.

The cortex of most stems, being above
ground where some light reaches it, has
cells that are green. As the stem grows
older, just as in roots, cork tissue is
formed from cortex cells just inside the
epidermis. This cork tissue cuts off the
water supply from the epidermis and
kills it, leaving cork on the outside. The
stomata which are present in the epi-
dermis become lost and new openings
through the cork, called lenticels, form.

Fig. 177 Note
the boles in
the sieve
plate ivhich
lies between
the tipper
and lower
cell. Sieve
tubes carry
manufac-
tured food
through
plants. See
pages /57-
ijS.

Cork is not formed in the stems of some
herbs. In most herbs it is only a thin
layer, but in many woody stems the
cork layer becomes quite thick. The
cork oak that is native to Spain forms a
cork layer that may become several
inches in thickness. It is this tissue that
is cut into cork stoppers. In some trees
new layers of cork form, first from cor-
tex cells nearer the phloem and then from
the phloem cells themselves. All the orig-
inal cortex cells and then the older
phloem cells thus are cut off from a
supply of water and die. The bark of
such trees is rougrh and furrowed. The
cortex of birch and certain other trees
lasts for a long time. Their bark is smooth
except in old trees. In beech the cortex

154

All Food Is Made by Green Flants unit hi

Fig. 178 (left) The smooth paperlike bark of
the birch with its conspicuous leiiticels. Can yon
name another tree ivhose young tivigs have con-
spicuous lenticels? (Schneider and schwartz)

Fin. 179 (below) Diagram of a young ivoody
stem. How does this steTU differ from most
root si' Wl:iat are the parts of the vascular

c y Under?

is never lost; the tree keeps a smooth bark
throughout its Hfe.

The vascular cylinder is much like the
one in roots. It consists of phloem, cam- Epidermis
bium, and xylem. But in the center there Cork
is usualK' a fourth cylinder of thin- Cortex
walled cells, the pith. Pith is very rarel\'
found in roots but is found in most
stems. Compare Figures 176 and 179.
This vascular cylinder connects at its
lower end with the vascular cylinder of
the roots. At its upper end it branches Xylem
many times and in each leaf branches
again, forming the veins of the leaves. Cambium
You will find it interesting to study a
young stem as described in Exercise 8.

How stems grow longer and branch. A Cortex
swing fastened to one of the lower limbs
of a tree remains the same distance from
the ground \ear after year; yet the tree
jrrows taller all the time. FA'idently the
lower portion of the trunk docs not
lengthen. In fact, the tree lengthens only
near its tip. In parts of the world where
there are distinct seasons growth ceases
during the winter. At this time the cells
at the tip of the stem arc covered by
heavy scales, forming the tennincil bud.

Lentice

PROBLEM 2. The Fart Stems ami Roots Play hi Making Food

M'5

V\G. 1 80 There is variety in
water-condiicting tubes. A
and B are found in conifers
{they are called tracheids);
C is a tube foimd in flow-
ering plants. The walls are
thickened in different ways.

See Figure 181. If twigs are available
study one carefully by doing Exer-
cise 9.

Along the sides of the stem are lateral
buds containing cells which can grow
into stems and leaves. In the spring, when
growth begins again some of the lateral
buds develop into branches. These stems,
like the main stem, lengthen near the tip,
form lateral buds, and before the end of
the season form a terminal bud. Thus
each year the branches extend farther
and farther out from the trunk and each
branch forms branches along its sides.
When a plant lives for many years it may
become very tall and wide-spreading.
We see that both stems and roots grow
in length only at the tips.

How stems grow in width. In dicot trees
and shrubs the growing tips are notice-
ably thinner than other parts of the
stem. The thickest part of the tree trunk
is at the very bottom; the thickest part
of a branch is at its base. The fact that
the older parts of a stem are thicker than
the newer or younger parts is good evi-
dence that the stem of a tree or shrub is

Terminal bud

Lenticels

Scars made by
scales of last
year's terminal

bud

Lateral bud

Leaf scars

The tubes through
which sap traveled
into the leaves

Fig. 18 1 Tip of horse chestimt twig, about nat-
ural size. At what poi?7t woidd such a stem grow
in length? How crnt you tell how much this
stem increased in lejigth during one season?
Find the lateral buds. Find where leaves hai'e
been attached. Where do lateral buds arise with
relation to the leaves?

156

All Food Is Made by Gree?i Pimm unit hi

constantly growing in diameter (width)
throughout its entire length.

The growth in thickness is the result
of the activity of the microscopic layer
of cambium between the phloem and
xylem. At the end of the w inter when
the ground thaws, or at the beginning of
the rainy season where there is no frost,
water again enters the roots, and sap be-
gins to flow upward. I'hcn the cells of
the cambium divide actively and form
thick-walled xylem tubes and fibers to-
ward the inside. At the same time they
produce more of the sieve tubes and
fibers toward the outside. See Fig. 179,
page 1 54. The xylem tubes formed in the
spring of the year are wider cells than

Fig. 183 (above) Cross section of a 30-year-old
part of a tree. How can its age be told? Notice
the dark center portion, called heartwood, and
the lighter outer portions, called sapwood.
Notice, too, that the thickness of the annual
ririgs varies. Can you think of some reason for
this variation?

Fig. 182 (left) California redwoods. So?ne of
these were already tall trees when Columbzis dis-
covered Afnerica. How do we know this? (u. s.

DEPARTMENT OF INTERIOR)

those formed in the late summer. Even
to the naked eye the spring growth looks
quite different from the summer growth.
The narrow cells formed late in the sea-
son show as a darker "ring" (cylinder).
These double rings are called aimiial
ri?igs. By counting them one can learn
how old that part of the tree is. There
are, of course, more rings at the base
than near the top of a tree. No rings
appear in the phloem region because
there is no difference in size of phloem
cells that are formed in spring and sum-
mer. The cork of most trees likewise
has no annual rings but in birch bark
cork the cells made in spring are thinner
walled than those made in summer; that

PROBLEM 2. The Van Stems a?id Roots Flay hi Makhig Food

is why birch bark peels into thin sheets.
This growth in thickness is known as sec-
ondary thickness or secondary growth.
As it continues only the younger xylem
and phloem cells are active. To test your
knowledge of stem structure and growth
do Exercises io and ii. In some trunks
the number of annual rings cannot be
counted because the heartwood may dis-
appear, leaving the tree hollow.

Stem variations. You have studied
woody stems of dicots. Herbaceous
stems of dicots have the same kinds of
tissues but in different amounts. There
is usually more cortical tissue and less
cork. Some herbaceous stems make little
or no cork. Also in most herbaceous
stems there is a larger proportion of
pith and some have more fibers in or
near the phloem than is usual in woody
stems. The xylem and phloem with cam-
bium between them, along with some
fibers, are found in bundles located in
a ring around the pith. These are called
vascular bundles. Pith tissue extends out
between the bundles.

In monocotyledons, whether they are
herbs, shrubs, or trees, the separate vas-
cular bundles are not usually arranged
in a ring. They are scattered through the
pith. You will note other differences
when you do Exercise 12. Monocots
rarely have cambium and do not, in
general, have secondary thickening. The
stem of the bamboo and the trunks of
many palms have the same diameter
along their entire length.

Movement through xylem and phloem.
Xylem is continuous from the root
through the stem, through its branches,
its finer twigs, and into the veins of the
leaves. See Figure 185. That is, there is a

157

Fig. 184 The vascular bujidles in a corn stem.
Corn is a moJiocot. How do these vascular
bundles compare m position with the vascular
bundles i?i a young dicot stem? Where is the
pith? (blakiston)

continuous passageway of xylem tubes
starting underground and ending among
the green cells of the leaf. Water from
the soil travels up through these tubes.
When there is enough water in the soil
there is a nearly constant stream of water,
containing some of the dissolved minerals,
through the xylem tubes. And the flow is
always upward.

Sieve tubes, too, are continuous from
the root, through the stem and directly
into the various parts of the leaf. Only

158

All Food Is Made by Green Flams unit hi

■•-^-^-^-y-: J

Fig. 185 The hickory leaflet (part of a compound leaf) was treated to remove all
tissues except the veins and epidermis. The dark spots are diseased areas. The smallest
veins co?2taiji both xylem and phloem. They are connected through the larger vein
and the leafstalk to similar tissues iit the stem and roots, (hugh spencer)

manufactured products and some min-
erals from the soil travel through the sieve
tubes of the phloem. Sugar made in the
leaves may move down through the sieve
tubes to the roots in large amounts. It
may accumulate there as sugar or starch
and form a thickened, fleshy root. Or the
sugar may be combined with minerals
into protein; this can happen in any part
of the plant. Passage of sugar and minerals
through sieve tubes may be up or down.
But proteins, fats, and starches cannot
move by diffusion since thev^ are insol-
uble and the protoplasm of the cell is not
permeable to them. In general, they are
manufactured within the cell in which
they are found. All three, however, may
be made soluble (digested) in the cells
and the soluble products ma\' then move
to other parts of the plant.

Digestion of insoluble foods in plants.
Most of us are quite aware that digestion
of insoluble foods occurs in animals. We
have a digestive system (see page 1S8) in
which insoluble foods are made soluble.

Plants, too, have digestion although they
have no digestive system. During the
daytime starch accumulates in the leaves
and green stems of plants. Much of this
accumulated starch is digested to sugar
which moves to other parts of the plant
durintr the night. In temperate climates,
starch, protein, and fats accumulate in
stems, roots, and seeds in the summer.
This insoluble food is dio-ested the fol-
lowing spring and the soluble products
are used in tiX new growth of young
stems, leaves, roots, and seedlings. You
will study about digestion in the next
unit.

The forces that move water in plants.
Water and mineral compounds enter the
epidermis of the root by diffusion, largely
through the root hairs. They pass by
diffusion across the cortex and outer
part of the vascular cylinder from cell
to cell. Here the water enters the xylem
tubes. As long as the water supply lasts
in the soil, more and more water diffuses
into the xylem tubes. The water then

PROBLEM 2

The Part Ste?ns a?hi Roots Flay hi Making Food 159

rises in each xylem tube. You may have
seen water rising several feet in a thistle
tube in the experiment showing diffusion
through a membrane. But our problem
now is to explain the rise of water not
three or four feet but a hundred feet or
three hundred feet in tall trees. How
does it get to the leaves at the very top
of a tree?

It has been known for a long time that
if a very narrow tube is dipped into
water the water will rise in the tube.
The narrower the tube the higher the
water will rise. This is called capillary
action; the narrow tube is called a capil-
lary tube. Water may rise in each xylem
tube by capillary action. This tube,
though extremely long, is the finest kind
of capillary tube for it is microscopic in
diameter. It is the width of only one
cell. Since it is so fine a tube, water read-
ily rises in it for some distance. Do Ex-
ercise 13 to see capillary action.

Another force that causes water to
rise in xylem tubes was discovered about
thirty years ago. It was discovered that
water in a capillary tube stays together
in a column as if it were a wire. If some
kind of pull is given at the upper end of
such a column the whole column moves
up.

The pull on the water in the xylem
tubes. Take another look at Fig. 185, page
158. What the picture does not show
is that the veins with their vascular tissue
divide into such tiny branches that but
very few cells lie between any two of
the tiniest veins. Water coming up
through the xylem tubes constantly dif-
fuses from the tubes to the neighboring
cells. All the leaf cells, including the
epidermal cells, hokl large quantities of

water both in the protoplasm and in the
cell wall. Now if the concentration of
water in the cells is greater than it is in
the surrounding atmosphere, the water
passes off into the air. We say the water
evaporates.

Very little of the water leaves directly
from the epidermal cells. Most of it goes
out from the air spaces through the sto-
mata. Every air space within the leaf is
surrounded by cells from which water
molecules are separating and diffusing as
water vapor. From the air spaces this
water vapor diffuses outward through
the stomata. Even when the stomata are
said to be completely closed there is
still enough of an opening for water
molecules to pass through. And at no
time would all the stomata of a plant be
completely closed. When water leaves
the cells and diifuses into the surround-
ing air we call the process transpiration.
If you have the equipment you will find
Exercises 14, 15, and 16 worth while.
Transpiration thus decreases the concen-
tration of water in the leaf cells near the
upper end of the water column in the
xvlem tubes. Water then diffuses from
the tubes into these leaf cells and thus
pulls on the column of water. Because
it is transpiration that decreases the con-
centration in the leaf cells this pull has
been called the lifting power of tran-
spiration.

Transpiration important to the farmer.
A single com plant may lose three or
four quarts of water on a hot day. A
birch tree with about 200,000 leaves loses
as much as 350 quarts on a hot dry day
in summer. These large amounts of water
vapor in the atmosphere condense in
time and come down as rain. Can you

i6o

All Food Is Made by Green Plants unit hi

Fig. 1 86 The barrel cactus
of our desert states is a good
example of a plant that loses
little water in the hot sun.
How do you explain this?

(U. S. DEPARTxMENT OF AGRI-
CULTURE)

5!%''-^j^^-

imagine the effect of square miles of
forest land? You can see, too, the effect
that transpiration has on the soil. The
small plot of soil in which the birch tree
grows would remain moist for a much
longer time if there were no tree. An
acre of barren soil loses water far more
slowly than the same acre planted to
grass.

But plants do not all lose water at the
same rate. The cactus in the desert may
lose only 0.02 of a quart in a day, in spite
of the desert heat which hastens evapora-
tion. There are two reasons for this.
There is little water in the soil and the
cactus usually has a very small surface.
Making practical use of this knowledge,

farmers plant crops like broomcorn with
a smaller leaf surface and extensive roots
in dry areas. Crops ^\hich lose \\'ater
rapidly can be planted in the moist soil
of the Eastern and Central states.

In a drought water is lost faster than
it diffuses into the plant; the plant wilts.
A cell well-filled with liquid is said to be
tiiTfrid. Turgid cells are swollen and firm.
If all the cells are turgid the plant is firm
or stiff. As water is lost, cells lose their
turgidity and the plant wilts. If this loss
continues for a long time, the plant dies.
Too rapid transpiration is responsible
for a great loss in crops. To test your
understanding of this paragraph do Ex-
KRCISF, 17.

PROIH.EM 2. The Part Ste?ris and Roots Flay in Making Food i6)

Questions

1. Draw in simple outline a taproot system and a fibrous root system.
Name several plants, the roots of which have large amounts of food.

2. Name several plants which have roots above ground.

3. What else makes up soil besides minerals? Name three substances
found in soil. What is soil water?

4. Where are root hairs found? Describe their microscopic structure.

5. What is diffusion? Explain how soil water enters a root hair. Re-
member to explain the movements of water and minerals separately.

6. Why can diffusion into a root hair continue indefinitely?

7. Name the three cylinders that make up the root, beginning with the
outermost. Where in the root is xylem found? Name two kinds of
cells that make up xylem. Where do you find phloem, sieve tubes,
and cambium? How do sieve tubes differ in structure from xylem
tubes?

8. Draw and label a cross section of a stem, showing the cylinders
usually found. What makes up the vascular cylinder? Explain how
in many older stems the cortex is finally lost.

9. How do stems grow in length? How do stems branch?

10. Explain why one can count the rings of wood to determine the age
of a tree. Why must one count the rings at the base of the trunk?
In a table show the difference between the stems and leaves of the
monocots and dicots.

11. Which substances pass through xylem tubes? Through sieve tubes?
In which direction is the passage in each kind of tube?

12. When and where in plants is starch made soluble?

13. What is capillary action? In which plant tissues does it occur?

14. Define transpiration. Through which structures does water leave the
plant? What is the connection between transpiration and the rise of
water through the stem?

15. Give some facts and figures to show that transpiration is important
to our lives.

Exercises

1. How do the roots of a young bean plant compare in extent with
the parts of the plant above ground? Uproot a voung bean plant raised
in sawdust and wash the root system clean. Measure the lengths of the
main stem and of the root. Now measure the spread of the longest
branches and of the longest side roots. Compare the total length of the
stems with that of the roots. Make a diagram to show the proportions.

2. To learn the difference in size of particles in various kinds of soil,
place a trowel full of ordinary soil in a tall cylinder. Add water until
the cylinder is full. Stir thoroughly. Let stand until the particles have

1 62 All Food Is Made by Green Plants unit hi

settled. Describe. Does anything float? If so, what is it? Use a hand lens
to examine the smaller particles.

3. Does ordinary soil contain air? Pour water into a large battery jar
until it is half full. Put a trowel full of soil at the bottom of the jar.
Watch. Explain.

4. How does soil water differ from pure water? Soak soil in a flower-
pot so that there is more water than the soil can hold. Let it stand for an
hour. By pressing the soil, pour off the extra water into a funnel lined
with a fine cloth. Collect the water that drips through. How does the
water Icjok? If it is not clear, filter it again through filter paper. Boil this
water in an evaporating dish until the water is evaporated. Does anything
remain?

5. To see root hairs, lay six mustard or radish seeds (peas or corn may
be used but will grow much more slowly) on moist blotting paper in a
saucer. Cover with a glass plate. Do not allow the blotting paper to dry.
Examine the roots everv^ day with a magnifying glass. Do not touch them.
Why? Record your observations. Root hairs will also grow on the new
roots of a Tradescantia cutting placed in a test tube of water.

6. You can learn something about root structure from a carrot. If
possible use young carrots with fresh stems and leaves. After cutting off
the tips of the roots place the carrots in a tumbler containing red ink in
water. After standing in the bright light for several hours one of the
carrots should be sectioned at various levels. Make a longitudinal section
through a second. Draw, indicating by means of red crayon, the regions
where water rises in the root. Compare with the diagram of the root in
the text. How does it differ? On your drawing label vascular cylinder,
cortex, epidermis, water tubes. In \\hich region do the stored carbo-
hydrates lie? How can you find out?

7. What is the structure of a young root? Gather some young fibrous
roots about tit inch in diameter. Scrape these with the fingernail. How
does this substance feel? What is left when you have removed this sub-
stance? What could you call the part that is left? Try to break it and
to tear it. What do you notice? Explain.

8. In woody dicot stems the tissues are in cylinders. You can easily see
the ends of these cylinders if you make a clean cut across the end of a
twig with a sharp knife or razor blade. Note the soft pith at the very
center. Which cylinder is outside the pith? Feel its inner and outer part.
Describe. The cambium lies between the two parts. Why do you not see
it? Outside the phloem in some twigs there is a ring of hard tissue, the
fibers, and farther out lying just inside the brown cork is the cortex
composed of soft tissue. If the twig is young enough you may be able
to see the transparent epidermis.

9. How much does a stem grow in length in one year? Examine a twig
which is not in leaf. Measure it from the large terminal bud to the first
circular scar on the twig. This scar marks the point where the season's

PROBLEM 2. The Fart Stems and Roots Flay in Making Food

growth began. It was made by the last year's termi-
nal bud. Do this with several twigs of the same spe-
cies. Are all the distances the same? What would
you have to do before you could draw general con-
clusions from your measurements?

10. How does a stem grow in thickness? Copy
Fissure 187, a longitudinal section through the pith
and wood of a five-year-old sapling. The bark is
not shown. At the bottom of your copy put the
numbers i to 5 using i to represent the wood pres-
ent when the tree started its existence. Five repre-
sents the most recently formed wood. Draw a cross
section at each of the levels a, b, c, and d. Where
ought you to cut the section to determine the full
age of a tree? What is the general shape of the
trunk? Why?

11. {a) Why should you not twist a wire tightly
around a young tree? {b) When you remove the
bark from a t:\\ig why does the wood lying just
underneath feel wet and slippery? {c) How can a
botanist by studying a cross section of a very old
tree know that the year 1750 in that particular re-
gion was a dry year and the year 1820 was a wet
one?

12. How does a monocotyledonous stem differ
from a dicotryledonous stem? Cross and longitudinal
sections of young cornstalks make good material
for the study of vascular bundles in a monocot stem.
How many bundles are there in your cornstalk?
Where are they? How do they feel? Describe the
covering of the stem.

13. How does the narrowness of a tube affect the
rise of water through it? Place hairlike glass tubes of
varying thickness into colored water. What differ-
ences do you note? Make accurate measurements
and record. With a magnifying glass examine the
top of the column in the widest tube. What do you notice? Explain.

14. Does water leave a plant? Use a vigorously growing potted plant.
Insert one of its branches into a large test tube (one inch diameter). Plug
the open end with cotton and suspend the tube in a clamp on a ring
stand. Water the plant and place in the light. What do you observe after
half an hour and again after several hours? Are you ready to draw con-
clusions? What else should you do?

15. How much water is lost by an actively transpiring plant? Water
a plant. Enclose the plant pot and the soil in a rubber sheet so that

163

Fig. 187 Diagram of
a longitudinal section
through a ^-year-old
woody stem. (See Ex-
ercise 10)

164 ^11 Food Is Made by Green Plants unit hi

water can be lost only through the leaves (and branches). Keep an accu-
rate record of weights. Discuss your method with the class before pro-
ceeding. Can you calculate the amount of water lost per square inch of
leaf surface per hour? Weigh the whole set-up at intervals of two or
more hours.

16. Is transpiration more rapid through one side of the leaf than the
other? Prepare a set-up like the one in Exercise 15. Use a plant with few
and large leaves. Be sure to state which kind of plant was used. Prevent
transpiration from one surface of the leaves by coating them with a thick
layer of petroleum jelly. Measure the amount of transpiration by weigh-
ing. Now coat the other side. Explain your results.

17. To test your understanding answer the following questions, (a) Do
you think the following statement is true? Why or why not? "Transpira-
tion increases with a larger amount of moisture in the soil, and the
amount of moisture in the soil in time increases with transpiration."
(b) What else besides the amount of moisture in the soil determines the
amount of transpiration? (c) After watering it thoroughly, what else
might you do to help revive a wilted house plant?

Further Activities in Biology

1. How does the lack of minerals affect the plant? Plant pea seeds in
moist clean sand. When the seedlings are three inches high, transplant
them into the following solutions. (Only the roots should be under
water.)

Solution 1. (all minerals present)

Water (distilled) i liter

Calcium nitrate i gram

Magnesium sulphate 0.25 gram

Potassium acid phosphate 0.25 gram

Potassium chloride o.io gram

Ferric chloride 2 drops

Soh/tion 2. (no nitrogen) Use calcium sulphate instead of calcium

nitrate.
Solution 5. (no potassium) Use sodium chloride instead of potassium
chloride and monosodium acid phosphate instead of potassium acid
phosphate.
Solution 4. (no magnesium) Use calcium sulphate instead of magne-
sium sulphate.
Solution 5. (no calcium) Use sodium nitrate instead of calcium nitrate.
Solution 6. (no iron) Omit the ferric chloride.

How is the rate of growth affected by the lack of the various minerals?
Are all parts of the plant similarly affected? Make a chart showing your
results.

2. Using wax or any plastic substance make a model of a small root.

PROBLEM 2. The Part Stems and Roots Play in Makmg Food 165

3. Report on the economic importance of roots.

4. It would be interesting to see whether the amount of moisture af-
fects the development of root hairs. Raise germinated oat or mustard
seeds under different moisture conditions under glass.

5. You could show the class the result of sprinkling salt or too much
fertilizer on the soil in a pot of growing seedlings. (Plant 20 or 30 lentils.
Let them grow until they are two or three inches tall.) Could you set up
an experiment with a thistle tube to explain what happens?

6. Are epidermal cells completely waterproof? Some leaves, such as
apple and barberry, have no stomata on the upper surface. Find out
whether any transpiration goes on. (Cobalt paper turns red when moist.)

7. Does light affect the rate of transpiration? Can you devise an ex-
periment to find the answer?

8. If willow twigs are available you can make a whistle and find out
at the same time where the cambium lies. Gently pound a short piece of
stem all around. Thus you can separate the wood from the bark and
remove it.

hi UNIT IV you will consider these problems:

Problem i . How Can We Choose Foods Wisely?

Problem 2. How Does the Digestive System Make Foods
Usable?

Problem 3. How Are Materials Moved to and from Our Body
Cells?

Problem 4. How Are All Our Cells Provided with a Constant
Supply of Oxygen?

Problem 5. How Does the Body Get Rid of Wastes Formed
by Cell Activity?

Problem 6. What Substances Help Regulate Cell Activities?

UNIT IV HOW A COMPLEX ANIMAL USES FOOD FOR

ENERGY AND GROWTH

Fig. 1 88 }'oiir body consists of billions of liviv^ cells, each of ivhich Diust have a con-
stant supply of food. There seevis little connection between the foods on these shelves,
all made by plants or by animals that ate plants, and the cells in your brain, your arm,
and your toe. Can you explain how your body cells are kept alive and active by food?

(RALPH CRANE FROM BLACK STAr)

PROBLEM 1 Hoxv Can We Choose Foods Wisely?

TTie food of living things. You learned
earlier that all living things are made of
protoplasm and that all need the same
compounds, namely, proteins, fats, car-
bohydrates, mineral matter, and water.
The vitamins that you will read about
later are also needed. Carbohydrates are
oxidized and release energy. Fats and
more rarely proteins are used for oxida-
tion too. Proteins, the only food com-
pounds containing nitrogen, are always
needed for building up new protoplasm
by assimilation.

The source of man's foods. You have
read, too, that green plants provide the
necessary food for all animals; that the
chlorophyll manufactures sugar (photo-
synthesis); that the sugar may be con-
verted to starch, or to fats; and that the
sugar may combine with minerals in the
plant in making proteins. Animals get
all their food from plants, either directly
or indirectly. Either they eat plants or
they eat animals which had eaten plants.
Thus all animals, including man, are de-
pendent on green plants for the com-
pounds used in assimilation and oxidation
and thus for the energy to live.

Two meanings of "food." We eat beef-
steak, potatoes, vegetable soup, and hun-
dreds of other substances. These are the
things we think of as our "foods." Each
food has a slightly different make-up and
a different taste from every other food.

Yet, in all our foods we get the same
kinds of compounds over and over again.
They are proteins, sugars, starches, fats,
minerals, water, and vitamins. These
compounds in their soluble form enter
the cells where they keep the protoplasm
alive. They are the real food of the plant
and the animal. You see, therefore, the
word "food" means one thing to the
restaurant keeper, the butcher, and the
housewife. It means something different
in the laboratory and in the classroom.
When we think in terms of billions of
cells of the body, the word "food" means
the essential compounds which make up
the beefsteak, potatoes, and other things
served to us at the table. In some books
the word "nutrient" is used as a name
for these compounds used by the cell.

Why is it helpful to make a study of
common foods? Throughout the world
people eat the foods they are accustomed
to eat because of family habit, or they
choose foods that are easy to get or that
they like. Sometimes they eat certain
foods as a fad or because they think the
foods have some special value. This was
particularly true before there was a
scientific study of diet and it is still true
of large numbers of people. Since most
people appear to be healthy, the diets
they follow must be satisfactory in the
main. But a great many people are really
not as healthy as they could be if they

i68

Carbohydrates
Fats

Proteins

How a Complex Aji'wml Uses Food unit iv

Minerals

Water

Oxidation

#%■•

Assimilation

Fig. 189 Hoiv food coiiipoiinds are used by a livhig cell, hi what two ways are food
compounds jisedF Which coiiipotmds are used hi each process? Why are two arrows
drawn as darker lines?

were to eat the proper food in proper
amounts. Some are actually ill because
their diet does not contain the proper
foods. Others may succumb to infection
because poor diets do not make them as
resistant as they should be.

Since the beginning of this century
scientists have analyzed all our common
foods in the laboratory. They can tell us
what compounds are in the food and the
proportion of each. They can tell us
how much energy there is in a given
amount of each food. They can tell us
how each substance is used in the body
and how much of each is needed to keep
the body in good health. All of us can
now obtain this information. In this
book and in many others there are tables
showing the composition of some com-
mon foods. Use the table on page 172 to
answer the questions in Exercise i.

Measuring heat energy. To measure the
energy in a food substance it is necessary
to burn the substance. By oxidation
(burning) the chemical energy in the
substance is changed to heat energy. It
is then possible to measure the amount
of heat energy produced. The idea of

measuring heat energy may be new to
you. Do not confuse measuring temper-
ature with measuring heat energy. Heat
and temperature are not the same thing.
The difference between temperature
and heat can be understood if you con-
sider two cubes of iron, a small one that
measures one inch each way and a larger
cube that measures one foot each way.
If both cubes are at room temperature
and both are placed in the same hot oven,
the small cube will reach a high tempera-
ture long before the large one does. By
the time the small cube has reached a
temperature of 100° centigrade (boiling
temperature of water), the large cube
will only be warm. It takes much more
time and much more heat to raise the
temperature of the large cube to 100° C.
When both are at the same temperature
the large cube, therefore, contains much
more heat. You need not try to define
the words heat and temperature as long
as you understand this paragraph. Just
remember that heat is a form of energy;
it can be added to or taken away from
bodies, and as that is done the tempera-
ture of the body changes.

PROBLEM I . Hoiv to Choose Foods Wisely

169

Fig. 190 What was the original source of the
egg eaten by the skunk, and the ?nilk lapped up
by the cat? What is the source of all the food
eaten by animals? (johnson, Schneider and

SCHWARTZ, GEHR)

To measure anything there must be
a unit of measurement. Scientists have
agreed on a i^mit for heat energy. They
call it a 4^alo£ie[^ (k;al'-(>r5€TnT"'ir'the
amomi t^ of J ^p-^r rpqjiir ed to r aise the
temperature__jif_mTe kilogramTa"' little
FeUian one quart) of water one de-

g ree c entigiadj&>--Thus jtJa£x:i^TTes_^
to measure the am^mnt-o f heat by meas-
urin^g^'^with a thermometer the rise in
temT
tei

ire o f pure water. When the

risen 7 ° C, we say 7 Calories of h eat en-
ergy liad been addgd^-If you can do Ex-
ercise 2, you understand something
about the measurement of heat.

Measuring the energy in food. To find
out how much heat is produced when a
food compound is oxidized, some of the
pure substance is weighed so that the
experimenter knows exactly how much
is going to be burned. The substance is
then placed inside a chamber in which
it can be oxidized. This chamber is sur-
rounded by a jacket containing pure
water which catches every bit of heat
produced. The outside of the jacket is
covered with asbestos or some other ma-
terial that prevents escape of heat. The
temperature of the water is taken before
and after the oxidation. The amount of
water in the jacket is known. And, since
the experimenter knows how much the
temperature of this water rises, it is easy
to determine how many Calories were
produced by the burning (oxidation) of
that amount of food. In this way scien-
tists have determined the amount of heat
energy to be obtained from a known
amount of protein, carbohydrate, and
fat. The apparatus used is called a calo-
rimeter (cal'o-rim'e-ter).

Besides burning known amounts of
pure proteins, carbohydrates, and fats,
scientists have also tested most of the
common foods for their energy value.
For example, a thick slice of white bread
may be burned. If the thermometer
shows that the temperature of 1 1 kilo-

1 70

Fig. 191 Cross scctiuH uj a calorhiieter. M'l.icie
is the food burned''' Of what use is the ther-
mometer? The water is stirred by the electric
motor. Why is the outside wall of the calo-
rimeter so thick? (AMERICAN MUSEUM OF NAT-
URAL history)

grams of water has been raised 10° C by
oxidation of the bread, then we know
that this sHce of bread contained 1 10
Calories of heat energy.

Measuring energy output in man. There
is a device similar to the calorimeter de-
scribed above but so large that a person
can be placed in it and his heat output
measured. This apparatus, however, is
so costly that few have been built. In-
stead, the amount of heat produced by
a person is measured indirectly by meas-
uring the amount of carbon dioxide ex-
haled or the amount of oxygen inhaled.
By making various calculations, includ-
ing calculations as to the size and weight

How a Complex Ayimml Uses Food unit iv

of the person, physicians can determine
a person's heat production. These meas-
urements are made when a person has
not taken food for some hours and is
lying down at complete rest. The heat
production under these conditions is as
low as it can be; it indicates a person's
basal ?netabolisin. Aietabolisin means all
the chemical changes that go on in the
body. By basal metabolism we mean the
amount of metabolism when the body
is at rest. But even when the body is at
rest there are many active organs. The
heart continues to beat, breathing is con-
tinued, the digestive organs are doing
very little work but have not ceased
activity completely, and the brain and
some other parts of the body are still
doing some work. Besides, oxidation con-
tinues in every living cell.

In men the basal metabolism is some-
what higher than in women. It is highest
in young babies and grows less through-
out life. Naturally as a person becomes
more active or exercises, his metabolism
increases far above the basal level. In a
person living a normal life the actual
daily production and use of energy is
far above his basal metabolism. This
daily production of energy depends
upon a person's age, sex, size, weight,
t\'pes of activity, and health.

Calories in your diet. After growth
stops, the intake of Calories should equal
the output of Calories. If the number of
Calories supplied by the diet is larger
than the need for energy, the food sup-
plying these extra Calories is stored and
you put on \\cight. If \ow get fewer
Calories than you need, some of the food
stored in your body tissues is oxidized
and \'ou lose weight.

PROBLEM I . Honjo to Choosc Foods Wisely

171

Fig. 192 A basal metabolisDi
test. The apparatus measures
the amomit of oxygen used
by the girl while at rest.
How does the physician use
such data? (sanborn com-
pany)

A man of average size needs:

16 waking hours 1200 C (basal metabolism)
8 sleeping hours 500 C

Add to this the Calories required per
day according to occupation: Profes-
sional or business 600-1200; Mechanics
1 200-1 500; Athletes or laborers 1500-
4000.

The average businessman will need
about 1200 plus 500 plus 800 or 1000 (de-
pending on his activity). This adds up to
about 2500-2700 Calories per dav. Chil-
dren need more Calories in proportion
to their size because they are growing
and are usually more active than adults.
A 16-year-old boy may need more Cal-
ories than a much larger man engaged
in light work. You can roughly calculate

the number of Calories yoji need per day
by turning to Exercise 3.

Calculating the Calories in a meal. Some
years ago the enthusiasm of dietitians
(people who study diets) led some to
urge the housewife to study food tables
so that she might plan her meals scien-
tifically. But it was soon discovered that
this was a difficult task and not at all
necessary for the ordinary person. Nor-
mally, a person gets the right amount of
Calories by following his appetite, al-
though some young people get too few
Calories in their desire to keep their
weight down. Some older people ac-
quire the habit of overeating. It is well
to remember that it takes only 4000 extra
Calories to produce a pound of fat.

172

How a CoT/iplex Aii'wial Uses food unit iv

COMPOSITION

Carbo-

Protein

Fat

hydrate

Food

Measure

Calories

(%)

Cereals

(i) Bread, white, enriched

I slice, average

(2) Bread, whole wheat, 60%

I slice, average

(3) Cornmeal, bolted yellow

f cups, cooked

106

(4) Oats, rolled

1 cups, cooked

119

(5) Rice, white

1 cups, cooked

105

0.3

(6) Spaghetti, tomato sauce

I serving

271

Dairy Products

(7) Butter

I pat, average

0.6

0.4

(8) Cheese, American Cheddar

I ounce, average

112

(9) Ice cream, plain

^ quarts

210

(10) Milk, whole

6 ounces, med. glass

123

(11) Eggs, raw, whole

I medium, average

0.8

(12) Margarine, fortified

I tablespoon

0.6

0.4

Fruits and Nuts

•

(13) Apple, fresh

I large, 3" diam.

0-3

0.4

(14) Banana, fresh

I medium

I.O

0.2

(15) Grapefruit, fresh

^ small

0.5

0.2

(16) Grapes, American

I bunch, 22-24 aver.

1.0

(17) Orange, whole

I medium

0.9

0.2

(18) Prunes, dried

4-5 medium

149

2.0

0.6

(19) Peanuts, roasted

16-17 nuts

26.0

44.0

Meats and Fish

(20) Bacon, medium, cooked

I 5-inch strip, crisp

(21) Beef, round, fried

I slice, 3" X 2" X V

233

(22) Chicken, roasted

3 sHces, 3|" X 2V X i"

193

(23) Lamb chop, shoulder

I chop, 4" X sh" X r

245

(24) Liver, beef, fried

I slice, 2f " X 2" X fV

(25) Frankfurter, boiled

I, 5^" long, f" diam.

121

(26) Codfish cake

I cake, 2^" diameter

122

(27) Salmon, canned

f cup, scant

102

Vegetables

(28) Beans, navy, pea bean,

i cup, cooked

105

kidney, pinto

(29) Beans, snap

^ cup, cooked

0.2

(30) Cabbage, fresh, head

^-f cups, shredded

0.2

(31) Carrots, raw

I large, f cups, cubes

0.3

(32) Cauliflower, raw

4 rounded tablespoons

0.1

(33) Lettuce, head

I large leaf

(34) Onions, mature, raw

I large or 2-3 small

0.2

(35) Peas, fresh, raw

f cups shelled

lOI

0.4

(36) Potatoes, white, cooked

I medium in skin

129

0.1

(37) Potatoes, sweet, baked

I large

213

0.7

(38) Spinach, fresh

f cups, cooked

0-3

(39) Tomatoes, canned

i cup

0.2

Figures are given in round numbers. The daily diet for growing boys and girls
should include besides proteins, fats, and carbohydrates, the following sub-

Adajned from Food Values of Portions Covmionly Used bv Bowes, A. do P. and Church, C. F.

PROBLEM I. How to Choosc Foods Wisely
OF Foods *

173

Vitamin A

Thiamin

Riboflavin

Niacin

Ascorbic Acid

Vitamin D

{mg)

(mg)

I. If.

(»!Cg)

(meg)

(>ng)

(mg)

I.U.

(I)

•5

0.6

(2)

0.9

(3)

•3

0-3

(4)

1.6

165

0-3

(5)

0.4

(6)

I.O

1336

125

1.6

(7)

330

(8)

247

173

0.2

493

142

(9)

132

104

0.1

■540

190

0.1

(10)

212

167

0.1

288

306

0.2

(II)

105

1.4

570

170

(12)

trace

258-429

(13)

•5

135

(14)

430

0.6

(15)

•3

0.2

(16)

0.4

(17)

28s

120

0-3

(18)

1.9

945

0.8

(19)

■3

45 .

2.4

(20)

0-3

(21)

250

3-5

122

153

5-3

(22)

305

2.7

214

10.2

(23)

168

2-3

153

196

4.4

(24)

187

6.1

9600

115

1 190

6.8

(25)

1-4

III

135

1.2

(26)

130

0.7

(27)

173

108

3-9

275

(28) 44 139 3.1

180

0.6

(29)

I.I

630

100

0.6

(30)

•3

0.1

(31)

12000

0-5

(32)

0.4

(33)

(34)

•5

0.1

(35)

122

1.9

680

360

180

2.1

(36)

I.I

168

1.6

(37)

1.2

8287

143

I.I

(38)

9420

120

240

0.7

(39)

1050

0.7

stances represented in the above units: calcium, 1300; iron, 15; Vitamin A,
5000; thiamin, 1400; riboflavin, 2000; niacin, 14; ascorbic acid, 85.

174

Every person, however, should have
a good general idea of the composition
of common foods and of the comparative
number of Calories supplied by each.
In planning meals for babies and for
people who are not well or who are not
normal in weight, constant use of the
tables is desirable. By doing Exercises
4, 5, and 6 you will learn something
about planning meals.

What you should know about proteins.
It is generally agreed that a little over 50
per cent of the total Calories should come
from carbohydrates, about 30 per cent
from fat, and not less than 12 per cent
from protein. For the average person
there should be about 80 grams (3 oz) of
protein daily. Much of the protein is
used in assimilation. Therefore, during
active growth, children often need com-
paratively large amounts of protein.

There is something else you must
keep in mind about proteins besides the
amount. There are many kinds of pro-
teins, those in animal foods being more
like your body proteins than are the
proteins in plants. You have read that
when plants synthesize proteins they first
make simpler nitrogen compounds called
amino acids. Some twenty-odd amino
acids are known to chemists and the com-
binations of amino acids in plant foods
differ somewhat from those in animal
foods. In fact, certain amino acids are
completely lacking in most plant foods.
This means that most plant proteins do
not make adequate substitutes for animal
proteins. Wheat contains, among several
proteins, only one that is as useful as
animal proteins. Legumes (the various
beans and peas) contain much protein,
and the proteins are very good; this is

Honjo a Cojnplex Animal Uses Food unit iv

particularly true of soybeans. But with
these exceptions plant foods are not as
good sources of proteins as are meat, fish,
eggs, milk, and milk products, which are
the more expensive foods.

What you should know about carbohy-
drates and fats. You already know that
for the most part you depend on carbo-
hydrates and fats for your energy. Fats
provide more than twice as much energy
pound for pound as sugar and starch.
However, although fats contain more en-
ergy per pound than any other food, it
is not wise to eat large amounts of fat.
The body does not deal with them as
successfully as with other foods. Pro-
teins, if they are oxidized, give the same
amount of energy as carbohydrates. But
to get enough energy from lean meat you
would need many pounds daily; and meat
is always expensive. All in all, therefore,
carbohydrates are our best energy pro-
ducing foods. When energy is needed
immediately, there is no food as satis-
factory as sugar. Lumps of sugar and
bars of chocolate are often given to foot-
ball players before beginning a game.
And you know that, during a war, large
amounts of chocolate and other sweets
go to the armed forces. Alcohol provides
much energy for a short time, but it may
also reduce efficiency.

When carbohydrates and fats are not
oxidized they are usually converted into
body fat which accumulates under the
skin, in the muscles, and next to internal
tissues (see Fig. 157). Some fat tissue is
necessary to keep us warm, and when a
person is unable to eat because of illness
or lack of food the fat stored in these
tissues is changed back into substances
which can be oxidized, providing energy.

F'ROBLEM I. Honj^ to Choose Foods Wisely

Fig. 193 Expermients teach iimcb about
what inight have caused the differences

ING CO.)

But to keep on storing fat is useless. And
carrying this stored fat about Math you
at all times is not only useless; it becomes
tiring. Older people should be careful not
to permit too much fatty tissue to form.
It is important to note that when young
people are overweight the cause may not
be overeating of fat or carbohydrates.
This is discussed in a later unit. You can
now plan a day's meals which would pro-
vide the correct amounts and kinds of
carbohydrates, fats, and proteins.

Minerals and water in your diet. Min-
erals are of many kinds and have many
uses in the body. Certain minerals are
necessary for assimilation. Some, like cal-
cium and phosphorus compounds, are
needed for making bones and teeth. Iron
compounds are needed for making red
blood cells. Sodium, potassium, and cal-
cium affect the heartbeat. Magnesium,
calcium, and chlorides help indirectly in
digestion.

diet. If the rats are of the same age and sex,
in weight and appearance? (general bak-

FiG. 194 These rats of the saiiie sex were horn
in the same litter. At 22 weeks of age one
weighed 2\ times as vmch as the other. Their
diet differed in ofity one respect. The large rat
received more calcium. What conclusions can
you draw? (u. s. department of agriculture)

In any ordinary diet you get enough
sodium, potassium, magnesium, and phos-
phorus. But it is wise to make sure of
obtaining sufficient calcium, iron, and
iodine. The table on page 172 shows in
which foods you may obtain calcium and

176 How a Complex Animal Uses Food

iron. Iodine, which is needed to prevent
goiter, is best obtained from fish and
other sea food. To review this informa-
tion do Exercise 7.

Water is still another substance needed
by the body. To begin with, it helps in
assimilation. Then, too, it helps in dis-
solving substances so that thev can move
around by the process of diffusion. You
should drink a considerable amount of
water each day.

What else is needed in the diet? Foods
contain proteins, carbohydrates, fats,
minerals, and water; but they contain
other useful substances too. They have
minute amounts of many different com-
pounds which add flavor. These add to
your enjoyment of food. And foods that
come from plants have more or less cellu-
lose and woody substances making up
the walls of each cell. Potato skins are
made up largely of such materials. While
you obtain little nourishment from them
they are of considerable importance in
your diet. These substances are called
roughage. A certain amount of roughage
is valuable for making the intestines push
the food along. You will understand this
better when you have studied digestion.

But besides the flavoring and roughage,
foods contain still other compounds
which are not used directly in making
protoplasm or in oxidation. Yet, they are
necessary to v^ou. These substances are
the vitami?is (vye'te-mins). They were
discovered in the course of experiments
on diseases which had puzzled people for
centuries. There were mysterious out-
breaks of disease which seemed to have
something to do with diet. Only within
the last fifty years have these mysteries
been definitely cleared up.

UNIT IV

Fig. 195 The smaller guinea pig has scurvy.
What must have been lacking in its diet? (u. s.

DEPARTMENT OF AGRICULTURE)

Mysterious diseases caused by faulty
diet. In the dark ages men told of a serious
disease which sooner or later attacked
sailors on long voyages. Their muscles
ached, they became weaker and weaker,
and blood flowed from their noses. Often
they died. The disease was called scurvy.
No one knew whether they were poi-
soned by their food, which consisted
principally of salted meat and dry crack-
ers, or grew sick from long exposure to
the sea air. It was noted in England in the
eighteenth century that if sailors drank
the juice of lemons or limes, they did not
suffer from scurvy. The reason was not
understood. But to prevent further out-
breaks of the disease a law was passed in
England more than a century ago requir-
ing that a supply of lemons or limes be
taken on long voyages. This is why Eng-
lish sailors are called limeys.

Somewhat later the Japanese had simi-
lar disastrous experiences with another
disease, outbreaks of which occurred i/

PROBLEM I. How to Choose Foods Wisely

Fig. 196 This chicken has polyneuritis, a disease
like beriberi in man. How can it be cjired?

(ILLINOIS AGRICULTURAL EXPERIMENT STATION)

their navy in the nineteenth century.
This disease was not new either; it had
long been known in China, Japan, and
other eastern countries; it is called beri-
beri (ber'ree-ber'ree). It, too, results in
exhaustion and eventually in death. There
is no bleeding as in scurvy; there is numb-
ness and paralysis.

The diet of these sailors was largely
polished rice, the kind you ordinarily
eat. Thinking that the disease might be
caused by a faulty diet, the officials of
the Japanese navy, about 1880, ordered
that other foods be provided the men in
addition to polished rice. Very soon
thereafter beriberi outbreaks became less
frequent. Just what was wrong with the
original diet no one knew. The govern-
ment officials were content, since they
had hit on a better diet; but scientists
were not satisfied; their curiosity had
been aroused.

Experiments to clear up the mystery of
beriberi. Some years after the new diet

177

had been ordered and its good results had
been proved, a Dutch scientist by the
name of Eijkman (ike'-man) became in-
terested in beriberi. He was stationed in
one of the Dutch colonies in the East
Indies \\ here he daily saw hundreds suf-
fering from beriberi in the hospital. He
had noticed that chickens living on a diet
of polished rice showed the same eflFects
as the patients. He used chickens, there-
fore, in a carefully controlled experiment.
First, he fed many of the birds a diet
consisting only of polished rice. They
developed a disease very much like beri-
beri. Then he divided his birds into two
groups; with half he continued the diet
of polished rice; to the other half he
gave not only the polished rice but also
the "polishings" or coatings of the rice
which are removed when the rice goes
through the mill.

Shortly after they had received the
rice coatings this group of chickens re-
covered from the disease. The other
group died. Eijkman concluded that
there was something in the skin covering
the grain that prevented the disease.
When he ordered his patients to eat the
coatings of the rice, they too, recovered
from beriberi.

Other biologists studied the chemical
make-up of the rice polishings in an at-
tempt to find out what substance in them
prevented beriberi. In 1911 Casimir Funk,
a Polish biologist, extracted the substance
and called it a "vitamine." Later this word
was changed to vitamin and the sub-
stance was called vitamin B.

What other experiments showed that
vitamins existed? About this time scien-
tists made another discovery in nutrition
experiments on rats. They gave the rats

.78

measured amounts of pure carbohy-
drates, proteins, fats, minerals, and water.
By using the prepared substances instead
of ordinary foods they were able to con-
trol the amounts more accurately. To
their astonishment the rats developed an
eye disease, sickened, and died.

The experiment was repeated but this
time as soon as the rats became sick some
of them were given small amounts of
raw milk each day in addition to their
regular diet. These rats regained their
health and remained normal. It was plain
that rats needed something more than
proteins, fats, carbohydrates, minerals,
and water. Although the experimenters
did not know what that substance M'as,
the experiment indicated that it was con-
tained in raw milk. Also, it was apparent
that the substance was needed in small
amounts only. It was concluded that this
substance was a vitamin and it was given
the name of vitamin A.

In the meantime others had discovered
by experiment that the citrus fruits like
oranges and limes contain a vitamin which
prevents scurvy. This vitamin was called
vitamin C.

Beriberi, scurvy, and the eye disease
caused by lack of vitamin A are called
deficie?jcy diseases.

The importance of vitamins. These ex-
periments definitely established the pres-
ence of tiny amounts of important sub-
stances in our foods besides the well-
known food substances. There followed
a vast amount of experimentation which
still continues. Important discoveries fol-
lowed one another in close succession.
We now know of about a do7xn vitamins
necessary to our good health and our
general well being. By the time you read

How a Co?fiplex Aimjial Uses Food unit iv
this others may have been added to the

list. All of us must know the following
about each vitamin: the foods in which
it occurs; how we are affected by insuf-
ficient amounts of it; and to what extent
cooking or the aging of the food destroys
it. By applying this information we may
hope to keep ourselves much more fit.
Most of us are not likely to become af-
flicted with beriberi, scurvy, or the eye
disease described above because most of
us eat a variety of foods. In any normal,
fairly varied diet at least small amounts
of the necessary vitamins are almost sure
to appear. Our problem is to get the full
amount of each vitamin needed to keep
us in the best of health.

Vitamin A. Vitamin A is one of the
vitamins that can now be made in the
laboratory. It is composed of the same
three elements as carbohydrates (C,H,0).
In animals vitamin A is made in the liver.
But it can be made only if carotene
(care'o-teen) is present. Carotene is a
yellow substance found not only in car-
rots and other yellow vegetables and
fruits, but also in the green parts of all
plants. Vitamin A or the unchanged
carotene can accumulate in the liver, in
the fatty part of milk, in q^2, yolk, in
kidneys, and in the pancreas. h\\ of these
foods are, therefore, good sources of
vitamin A. And since your liver can make
vitamin A out of carotene, you can also
be sure of getting your supply of the
vitamin by eating yellow and green plant
foods. In spite of the many foods that
supply vitamin A, many people suffer
from a slight deficiency of it.

You read above that in rats, a defi-
ciency of vitamin A resulted in a serious
eye disease. In man, too, a serious vitamin

PROBLEM I . How to Choosc Foods Wisely

179

Fig. 197 This rat was fed a diet lackmg vitamin B.,. During six weeks of a diet rich in
vitamiji B.,, its weight increased from 6^ grains to 16^ grams. Why should several rats
be used in such an experime^it? Explain, (u. s. department of agriculture)

deficiency causes drying up of the tear
glands and damage to the eyes. And in-
sufficient amounts of vitamin A in the
body result in the inability of the eyes
to produce a substance called visual pur-
ple; this is needed for vision in dim light.
Furthermore vitamin A keeps the mu-
cous membranes of the body normal and
healthy.

The vitamin B complex. What was
formerly called vitamin B is really a group
of vitamins. The one in the group asso-
ciated with beriberi is now called vitamin
Bi or thiamin. People getting an insuf-
ficient amount of thiamin are easily fa-
tigued and have a poor appetite; this may
be followed by loss of weight, irrita-
bility, and mental depression, A defi-
ciency of thiamin in the diet is common.
The best concentrated sources of thia-
min are liver, wheat germ, and yeast. It
occurs quite abundantly in wheat, rice,

barley, peanuts, dried beans, peas, and
soybeans. Unfortunately, the grains are
often refined before they are used. In
the refining process the vitamins, which
are in the covering of the seed and in the
germ, are removed.

Niacin (formerly called nicotinic acid)
is another vitamin of this group. Defi-
ciency of niacin causes the disease known
as pellagra. In the United States alone
about 100,000 people suffer from this
disease. There have often been outbreaks
of pellagra in institutions where too strict
economy was practised and no fresh
vegetables, milk, or fruits were included
in the diet. A less marked deficiency
causes loss of appetite and a general
breakdown of morale. As in the case of
thiamin its best source is liver and yeast.
Other good sources are kidneys, sweet-
breads, milk, and cheese, as well as the
unrefined grains which contain thiamin.

i8o

How a Complex Annual Uses Food unit iv

111 M msfM

Fig. 198 The x-ray to the left was taken on Feb. 5. This child had a bad case uf rickets
as shown by the fuzzy edge of the two boTies in the arm. Treatment was begun. The
second x-ray was taken Jime 25. What dijfere?ice can you see in the ends of the arm
bones? What treat?nent was probably given the child? (general baking co.)

There are other vitamins in the vita-
min B complex: riboflavin, pyridoxin,
pantothenic acid, and others. All of them
dissolve readily in water and are often
lost in boiling. Thiamin may be added
to foods such as flour and bread. Add-
ing vitamins to food is called "enrich-
ing" it.

Vitamin C. This vitamin, associated
with scurvy, is now generally known as
ascorbic acid. It is not only sailors on
long voyages who have sufi^ered from
scurvy. Throughout the ages there have
been outbreaks of scurvy wherever and
whenever there have been wars, famines,
or minor shortages of fresh growing
foods. At all times mild deficiencies of
ascorbic acid are very common. It seems
to be needed for the fomiing of connec-
tive tissues in the walls of the blood ves-
sels.

The best sources of ascorbic acid are
grapefruit, oranges, and the other citrus

fruits. Parsley, tomatoes both canned
and raw, peppers, and raw cabbage are
particularly rich in it. Dried seeds like
peas and beans have no vitamin C, but
if they are allowed to sprout they form
it and become a good source. It is com-
pletely lacking in eggs and meat, though
very small amounts are found in liver and
milk. Spinach and broccoli contain large
amounts but much of the vitamin C is
lost in cooking.

Ascorbic acid (vitamin C) is the most
easily lost of all the vitamins. It dissolves
readily in water and is therefore lost if
the water in which vegetables are cooked
is thrown away. In the presence of acids,
however, heat and oxygen of the air
have less effect on the vitamin. For this
reason tomatoes, which contain much
acid, keep their ascorbic acid after being
exposed to the high temperatures of can-
ning. In commercial canning, and most
canning in the home, oxygen is excluded

PROBLEM I. How to Choosc Foods

'^^■f^^f-''\:m:mm

Fig. 199 Above is a pig suffering frov! rickets.
Below is the same pig after small daily doses of
cod liver oil. What did the oil supply? (Wis-
consin AGRICULTURAL EXPERIMENT STATION)

while heat is appHed. This, too, saves
some of the ascorbic acid. Adding soda
to boihng vegetables helps to destroy the
vitamin.

Vitamin D. The lack of vitamin D in
babies and young children causes rickets,
a condition in which the bones and teeth
remain soft and there are malformations
in the skeleton. Minerals containing cal-
cium and phosphorus are needed for
strength and rigidity in bones and teeth.
But these minerals cannot be used in the
body if vitamin D is lacking. Ordinary
milk contains both calcium and phos-
phorus but has very little vitamin D. In
fact, no natural food, even of the many
foods eaten by adults, contains very much
vitamin D.

But we have learned two important

Wisely 1 8 1

facts in recent years about vitamin D.
In the first place, fish oils such as halibut-
liver oil and cod-liver oil are excellent
sources of this vitamin. Thev are often
given particularly to babies to supply the
much needed vitamin D. In the second
place, many plant foods contain a sub-
stance {ergosterol) which turns into vi-
tamin D in the presence of the ultraviolet
rays of the sun. Many animal tissues
contain a similar substance {cholesterol).

Both plant and animal foods can be
exposed to ultraviolet light for the pro-
duction of vitamin D. Such exposure to
ultraviolet light is called irradiation
(ir-ray-dee-a'shun). Milk is often so
treated in fresh or evaporated form.
Bread is sometimes irradiated and so are
some of the cereals. But not all irradia-
tion is successful. Sometimes fish-liver
oils or yeast are irradiated and fed to
cows which then produce milk richer
in vitamin D.

We, being animals, contain this same
substance (cholesterol) which can be
turned into vitamin D. In the bright
sunshine, which contains ultraviolet light,
we are constantly making this vitamin.
That is why vitamin D is called the "sun-
shine vitamin," although, of course, sun-
shine contains no vitamin. Many people,
however, do not get enough sunshine.
The ultraviolet rays do not pass through
ordinary window glass. And those of us
who live in cities, particularly smoky
cities, and in climates with a long winter
season, lack the sunshine we need for
making vitamin D.

Vitamin D seems to be a vitamin of
which you can get too much. Vitamin
A, if taken in excess of one's needs, ac-
cumulates and can be used at a later time;

1 82 How a Complex Animal Uses Food unit iv

and most of the other vitamins if taken
in larger quantities than needed merely
pass through the body. Vitamin D has
been made in the laboratory.

To see whether you are getting your
needed supply of vitamins, list all the
foods you ate yesterday. Using the food
table state: (a) of which vitamins you
got a large amount; {b) of which you
got only small amounts; {c) which vita-
mins were probably lacking.

Other vitamins. Vitamin E complex has
been shown by experiment to be needed
by rats for reproduction, and probably
by most other animals, too. We know
that eggs produced by hens lacking E
complex do not hatch. What effect it
has on human beings we are not yet sure.
But it would seem wise to include it in
the diet. It is found in lettuce, carrots,
tomatoes, t<^^ yolks, peanut and other
oils, and in all whole-grain cereals.

Vitamin K is necessary for the proper
clotting of blood as you will learn later.
Its richest sovirce is the green leaves of
our common vegetables. Exercise 8 is a
very important exercise for you to do.

Loss of vitamins. The care and cooking
of food is as important to you as the
choice of food if you want to have your
full supply of vitamins. In general, ex-
posure to oxygen seems to destroy vita-
mins, and the higher the temperature the
more rapid is the destruction. Therefore,
keeping vegetables without refrigeration
means a steady and rapid loss. Vegetables
should, if possible, not be peeled or cut
up before cooking; the smaller the pieces
the more surface is exposed to oxyi^en.
Furthermore it is desirable to cook in
closed utensils because in this way air
is excluded. And since water contains air

Fig. 200 The Basic Seven. Everyo7ie should eat
a generojis serving jrom each group every day.
Can you explain, in the case of each group, why
these foods are included among the Basic
Seven?

(oxygen) until boiling drives it out, it

is best to start your vegetables in boiling

water.

Extreme heat, especially in the pres-
ence of oxygen, destroys some vitamins,
particularly vitamin C and vitamin A.
For this reason cooking should not be
continued longer than necessary and
should be done rapidly. This is possible
in a pressure cooker.

Most vitamins, with the exception of
vitamins A and D, are soluble in water.
We should, therefore, cook in small
amounts of water and whatever water is
left should be kept and used, since vita-
mins (and minerals) are dissolved in it.
Do Exercise 9.

Vitamin pills. It is true that by paying
for capsules one can get the known vita-
mins. However, there may be many un-
discovered vitamins in our foods which
are necessar\' to us. For this reason, as
well as for the sake of economy, it is
better to depend on natural foods than

PROBLEM I . How to Choosc Foods Wisely

on the drug store for one's vitamins. A
natural, widely varied diet should con-
tain all the vitamins that any of us will
need under normal conditions, except
possibly vitamin D. We must, how ever,

Review Table of Vitamins

.83

remember that the freshness and the
method of preparing foods are just as
important factors as the kinds of foods
selected. Before finishing this problem do
Exercises 10 and 1 1.

VITAMIN

foods Rich in
Vitamins

How Stable

Results of Defi-
ciency in Vitamins

Thiamin

Made by yeasts and

Whole grains, seed

Dissolves easily and

Loss of appetite, nerv-

or Bi

other fungi; can be ex-

germs, tomatoes,

in cooking goes into

ousness; beriberi

/// B

tracted from rice pol-

spinach; not much in

water; can withstand

complex

ishings; water soluble;

most vegetables;

heat of cooking if no

has been made in lab-

liver and yeast

alkali is present

oratory; little storage

Niacin

Made by green plants

Liver, meat, fish, milk,

Resistant to heat and

Pellagra

(Nicotinic

and yeast; has been

eggs, green vegeta-

exposure to air; in

acid)

made in laboratory;

bles, yeast, and to-

cooking goes into

In B

water soluble; stored

matoes

water

complex

in liver and muscle

Riboflavin

Can be extracted from

Same as niacin

Rather stable; in

Digestive disturb-

(origi-

milk, eggs, yeast, etc.;

cookmg goes into

ances, nervousness,

nally G)

stored in liver

water

and weakness

In B

complex

Not made in our body;

Citrus fruits, tomato,

Easily destroyed by

Retarded growth, ir-

Ascorbic

has been made in lab-

germinating seeds.

heat, especially when

ritability, lack of en-

acid

oratory; watersoluble;
no storage

and leafy vegetables

alkali present; rap-
idly destroyed in air;
dissolves in water

ergy, and scurvy

Body makes it from

Milk, milk products.

Resistant to much

Night blindness;

carotene; fat soluble;

eggs, liver, yellow

heat; destroyed

sometimes special eye

not water soluble;

vegetables, and green

slowly m air

infection

stored in liver

Made in skin under

leafy vegetables

Fish liver oils; very

Can withstand high

Poor teeth and rickets

ultraviolet light from

little in egg yolk;

temperatures

ergosterol; fat solu-

milk, butter, and

ble; not water soluble;

meat

stored in liver, kidneys,

and other body parts

Can be extracted from

Germ of grains; green

Can withstand high

Reproduction in rats

wheat germ; has been

vegetables, and eggs

temperatures and

fails

made in laboratory;

drying

fat soluble; stored

Made by bacteria in

In considerable

Rather stable

Blood does not clot.

intestine; fat soluble

amounts in most
foods

but it is not lack of
vitamin which starts
this condition

1 84 How a Cofnplex Aii'mial Uses Food unit iv

Questions

1. What are the two uses of food in all living things?

2. What is the original source of all foods eaten bv man? Explain.

3. In what two different ways can the word "food" be used?

4. Discuss how people get along without a knowledge of foods.

5. What energy change occurs in the oxidation of food? What is the
unit of measure for temperature? What is the unit of measure for
heat? How much heat does a Calorie represent?

6. What facts are obtained by the use of a calorimeter?

7. How do physicians determine your minimum energy output? What
is meant by metabolism? By basal metabolism? How does the basal
metabolism of men and women, old people and young people, differ?

8. An average-sized man doing sedentary work needs 2500-2700 Cal-
ories per day. Explain how this figure is obtained. Compare the en-
ergy needs of people of your age with the energy needs of adults.
When should Calorie tables be consulted?

9. Why should we not depend on fat, the most efficient fuel food, for
our chief source of energy? Which food compound is used largely
for energy release in the body?

10. Why are the proteins of animal foods better for us than plant pro-
teins? Which plant proteins are good substitutes?

11. What does the body do with carbohydrates and fats not used in
oxidation?

12. Of what special use to the body are calcium, phosphorus, iron and
iodine? Of which minerals are we likely to have a shortage in our
diet? For what purposes is water used in the diet?

13. Give examples of roughage. Of what advantage may it be to you?

14. What has long been known about the disease called scurvy? About
beriberi?

15. Explain the object, the method, the observations, and the conclusions
of Eijkman's famous experiments. Who named the substance extracted
from rice polishings? What was it called?

16. How was vitamin A discovered? What serious disease is caused by
lack of vitamin A?

17. What is meant by deficiency diseases? What facts must we all know
about the various vitamins?

18. In what part of the body is vitamin A made? From what is it made
in the body? What are the best food sources of vitamin A? How
does the lack of vitamin A affect us?

19. What do we now call the vitamin that prevents beriberi? What are the
early symptoms of an insufficient amount of this vitamin? Name the
four best sources of thiamin or B^. Name seeds of plants which serve
as food for man. Why are seeds good food for us? Which disease is
caused by a deficiency of niacin? Which foods are good sources of
niacin?

PROBLEM I . How to Choose Foods Wisely j g .

20. What do we now call vitamin C? From which foods do we generally
get most of our vitamin C? Which other foods are rich in vitamin
C? Name four ways in which much of the vitamin C is often de-
stroyed in the preparation of vegetables.

21. Explain fully what is needed for proper bone development. If sun-
shine contains no vitamin why is vitamin D called the sunshine vi-
tamin? Name three foods which are frequently irradiated and state
the effect on these foods.

22. What do we know about vitamins E and K?

23. List all precautions to be taken to save vitamins in keeping and pre-
paring foods.

24. Why should we not depend on vitamin pills for our supply of
vitamins?

Exercises

1. In what proportions are proteins, carbohydrates, and minerals found
in common foods? Using the table in the text answer the following
questions: Do animal or plant foods contain larger percentages of pro-
tein? Do animal or plant foods contain larger percentages of carbohy-
drates? What foods contain large amounts of such important minerals
as iron and calcium? In general, what are the differences in composition
between leafy vegetables and root vegetables? Caution: The table is not
complete. How does this affect your answers?

2. (a) A piece of hot iron when plunged into half a kilogram of water
raised the temperature of the water 6° C. How many Calories of heat
were added to the water? {b) How many Calories of heat would have to
be taken from a kilogram of water to lower its temperature from 75° C
to 69° C?

3. The average Calories required per hour for each pound of a per-
son's weight are about as follows:

In sleeping or lying awake \ Calories

Sitting I Calories

Typewriting ^ Calories

Standing | Calories

Walking at a moderate rate i| Calories

Active exercise if Calories

If you weigh 120 pounds and sleep 9 hours, you would require for those
9 hours 120 X 2 X 9 Calories. Decide about how many hours of the day
you spend in each kind of activity and, considering your weight, cal-
culate about how many Calories you need in 24 hours.

4. Select five foods one normal portion of which supplies more than
100 Calories. Arrange them in order according to the number of Calories
supplied, beginning with the highest.

1 86 ^ How a Co7nplex Aimnal Uses Food unit iv

5. Suppose that in the three meals in one day you ate 9 pieces of 60
per cent whole wheat bread, 5 average pats of butter, 2 sweet potatoes,
4 strips of bacon, a portion of rice and 2 bananas. How many Calories
would this supply? Explain why you would not recommend this diet.

6. id) Name five foods which your physician might tell you to cut
out of your diet if you had to reduce your weight. {Cazitioii: No one
should attempt to change his \\'eight except under a physician's guid-
ance.) {b) Consult your family and friends for other "rules" for losing;
weight. By reasoning and consulting your tables see whether you can
find any scientific basis for their statements.

7. B^' consulting your text, including the food table, make a table in
your notebook as follows: In the first column list vertically calcium,
iron, phosphorus, iodine, sodium, potassium, and magnesium; in the
second column next to each mineral state how it is used; in a third
column state which foods contain the mineral in large amounts.

8. Using the chart, page 172, or a more complete food table, list in a
vertical column the foods available to you that provide the largest
amounts of each of these vitamins: thiamin, niacin, ascorbic acid, vitamin
x\, and vitamin D. You should then learn this list by heart.

9. Answer the following: {a) When a baby's diet consists only of
pasteurized milk, what food should be added to the diet? Why? [b) Ex-
plain why factory canned vegetables are presumed to be better for you
than those cooked by an inexperienced cook.

10. There are fads in diet as in everything else. By talking to your
friends, see how many of these you can learn about. Discuss each one in
class, in order to discover, if you can, whether there is any scientific
basis for it. In some cases it will be possible for you to test the truth of
a statement by experiment.

1 1 . Study the advertisements of foods in cars, magazines, etc. Copy
them exactly and bring your copy to class for discussion. To what
extent are these advertisements scientific? To what extent can you trust
them? What information should you get about these advertised foods?

Further Activities in Biology

1. As you know, the diets of various peoples difi^er. Make a critical
report on the diets of several national or religious groups, like the Eski-
mos, Arabs, Jews, Germans, Yankees, etc.

2. If your school has no charts showing the percentage composition of
common foods, a group might make some. Draw the outline of common
foods such as a rib roast, a fish, glass of milk, carrot, etc. By consulting
the table show the proportion of protein, fat, carbohydrate, mineral, and
water (including waste) in each food. Use difi^erent colors to indicate
each food substance.

3. A few of you working together can determine the efi^ect of the lack
of vitamins upon certain animals. Report the results of \()ur work to

PROBLEM 1. How to Ckoosc Foods Wisely 187

your class or club. If you have a school science paper, have your re-
sults published. There are a few points that all of these experiments have
in common that you ought to know. You must choose animals that are
in a good state of health. Wherever possible, the animals should be from
the same litter and of the same sex. The animals are then divided into
two equal groups. One group receives the diet lacking a particular vitamin
while the other group gets the same diet plus the vitamin. You must re-
member that the conditions under which you keep the animals are as
much a part of the experiment as the diet which you feed them. There-
fore, keep them under normal conditions of temperature and in clean
cages. Always keep an accurate daily record. Do not cause animals pain
or permit them to suffer. These experiments and others can be performed
without harm to the experimental animals if you change the diet as soon
as evidence of the effect of poor diet is obtained.

4. What is the effect of the lack of vitamin A upon rats?* Choose
rats about three weeks old. Feed one group a diet consisting of the fol-
lowing:

Casein (pure protein) 20%

Lard (fat) 15%

Starch (carbohydrate) 56%

Yeast (for vitamin B) 5%

Salt mixture (for minerals) 4%

The salt mixture should be mixed with the other food. Your teacher
will help you to get the chemicals you need to make the salt mixture.

Sodium chloride (NaCl) 5.19 gm

Magnesium sulphate (MgSO^-yH^O) 16.00 gm

Sodium dihydrogen phosphate (NaH,PO^-H,0) 10.41 gm

Potassium hydrogen phosphate (K^HPO^) 28.62 gm

Calcium lactate 39.00 gm

Ferric lactate 3.54 gm

The other group is fed butter instead of lard. When you have achieved
your results, return both groups to a normal diet.

5. What is the effect of the lack of vitamin C upon guinea pigs.^ Feed
one group a diet consisting of oatmeal, sterile hay, pasteurized milk, and
water. Add orange juice to the diet of the second group. Do the two
groups begin to show any signs of difference in activity, in weight, in the
condition of the fur? If so, add orange juice to the diet of the first group.
How long does it take for recovery?

* These diets are taken from Adventures in Biology, New York Association of
Biology Teachers.

PROBLEM A How Does the Digestive System Make

Foods Usable?

Food in the digestive tube. The food you
swallow enters a long, irregular tube
which runs right through your body.
This is the digestive tube. It is also called
the alimeiitary (al-i-men'tary) cmial. The
tube is narrow in some parts, wider in
others. In a person of average size it is
about thirty feet long; evidently it must
be coiled, at least along part of its length.
From the diagram, Figure 201, you can
learn that food goes from the mouth
through the throat into a long straight
food pipe (oocp/.ijgz/5 — ee-sof'a-gus).
This connects with the stomach. As you
continue your meal the food collects in
the stomach where it remains for some
time. The last of it does not leave until
two to four hours after eating. The food
does not lie quietly in the stomach. It is
being squeezed and moved around until
it is a pulpy mass. Then the stomach be-
gins to push the food, bit by bit, into the
long narrow tube known as the small in-
testine. You can readily see that this is
coiled. It, too, has muscular walls and by
their contraction the food is pushed along
the twenty feet of narrow tubing. It
takes about another eight hours before
the last of the meal has reached the large
intestine. The large intestine, or colon,
is a much wider and shorter tube into
which the small intestine opens at the
lower right-hand side of the abdominal

cavity. Here lies the appendix, a small
fingerlike pocket attached to the large in-
testine. The large intestine extends up the
right side, across the abdomen under the
stomach and liver and down the left side,
ending in the rectum. The rectum opens
to the exterior by an opening known as
the anus. It took you a few minutes to
trace these parts of the digestive tube. For
a meal to travel the length of this tube
takes twelve hours or more. If possible
examine a model (manikin) or large chart
of the digestive tube.

What happens to food in the digestive
tube? Food in the digestive tube is not
yet really in your body at all. It is merely
in a tube that runs through your body.
Yet the billions of cells in your brain, in
your hands, in your heart, all over your
body need this food to carry on oxidation
and other activities. How does the food
get to them? Of course, the blood carries
it. Our problem, then, is to learn how
food gets from the digestive tube into
the blood. The walls of the tube are made
up of many layers of cells. Blood vessels
lie among these cells. By the time the
meal you ate reaches the large intestine
most of it has diffused through the walls
of the tube into the blood stream.

When you studied diffusion you
learned that water, some minerals, and
simple sugars pass through cell mem-

PROBLEM 2. The Digestive Syste?n Makes Food Usable

189

Fig. 201 Mail's digestive sys-
te7n. The organs are not
drawn in correct proportion
or in exact position. Food
masses are indicated in the
stoviacb and at the lower
end of the small intestijie.
How long does it take food
to travel the full length of
the alimentary canal? What
digestive organs are show?i
that are not part of the
canal?

Mouth

Windpipe
(frac/ieaj

Liver —
fporf/y lifted)

Gall bladd

Large
intestine

Food mass
Appendix

branes. But the more complex sugars,
the starches, the proteins, and the fats do
not diffuse through cell membranes. Make
an artificial cell and see for yourself
whether starch, for example, is able to
enter it. See Exercise i. Those food com-
pounds that do not diffuse through a cell
are first digested in the tube and then
pass into the blood.

What is digestion? You have just read
that starches, proteins, fats, and some of
the more complex sugars are changed in
the digestive tube. Without this change
they could not get into the blood nor
could they later be used by the body

Salivary glands

Food pipe
foesopfjogus)

Stomach
Food mass

Pancreas

Small
intestine

Rectum

cells for oxidation and assimilation. The
chemists would say that the molecules
of protein, starch, fat, and some of the
sugars are large. These large molecules
are broken up into smaller molecules
making new substances. The process by
which the large molecules are changed
into smaller molecules of other substances
is called digestion.

Digestion is a chemical change; that is,
it changes the nature of the substances
that are digested. If a piece of bread is
broken into crumbs the change is a phys-
ical change. The crumbs are still bread.
No matter how tiny the crumbs may be

How a Complex Ajiimal Uses Food unit iv

190

made, it is still a physical change. The
nature of the crumbs is still the same.
But if the starch in the bread is con-
verted to some other substance the
change is chemical. The nature of the
starch has been changed.

End products of digestion. An interest-
ing and important fact about digestion
is that it occurs in steps. A food sub-
stance is first changed into smaller mole-
cules; then these molecules are changed
into still smaller molecules. These are
called mtermediate products of digestion.
Finally the substance is changed into
molecules small enough to diffuse into
cells and to be usable by them. These
last products of digestion are called efid
products.

There are other interesting facts about
digestion. You may eat proteins from a
hundred different kinds of animals and
plants. The proteins are all slightly dif- The starch is changed to a sugar called
ferent from one another. And all of them maltose. Exercise 2 will show this,
are so different from your body proteins Saliva has been studied carefully and

that they could not be changed directly found to contain a small amount of a
into your body proteins even if they substance that can change starch to malt-
could diffuse into your cells. In digestion ose. The substance in saliva that changes
all of these many different kinds of pro- starch to maltose is called ptyalin (ty'a-
teins from various organisms are broken lin).

up into the same few compounds. These What is an enzyme? An enzyme is a

simpler chemical compounds which are substance made by a living cell. It acts
the end products of protein digestion are on another substance in such a way as

are broken up or digested in the body.
You see then that they arc all made out
of the same twenty odd building stones
or amino acids.

In a similar way carbohydrates and
fats, too, are broken up into a relatively
small number of end products. No matter
what kinds of carbohydrates are broken
down or where they come from, the
same few end products are always pro-
duced. All fats, too, from every kind of
animal or plant are broken down into the
same few end products. And the end
products are the same whether the proc-
ess occurs in us or in a dog or in any
other kind of animal.

Digestion shown in a test tube. If you
mix some saliva with a little cooked
starch in a test tube and warm the tube
in vour hand for four or five minutes,
digestion of almost all the starch occurs.

called amino acids. Do you remember
that plants in building up proteins first
make amino acids? It may help you to
think of amino acids as "building stones"
of proteins. A large variety of buildings
may be built out of the same kinds of
stones. It should not surprise you then

to cause a chemical change in it. The
enzyme itself is not changed. Thus, given
time, a small amount of an enzyme can
change a \'crv large amount of a sub-
stance, since throughout, it remains just
as it was originally. Chemists are familiar
with substances that behave in this way

that a large variety of proteins can be in the laboratory. There are many of
built out of the same few amino acids, them. They call all of them catalysts
This is shown when the various proteins (cat'a-lists), and reserve the name en-

PROBLEM 2. The Digestive System Alakes Food Usable

Mucous membrane Stomach cavity

191

»ieMS'"'«:/jii' '"«sff

Sections of capillaries

Fig. 202 A magnified section through the lining
of the stomach. Four tiny glands are shown.
What lines each gland? The juice secreted
flows into the stomach cavity.

zyme for the special catalysts that are
made in a living organism.

The enzymes that change food sub-
stances into other and simpler substances
are called digestive enzymes. Ptyalin is
one of these. Many different digestive
enzymes are produced in the human
body; each digests, that is, changes some
particular food substance into simpler
compounds. One set of enzymes digests
protein, another fat, another starch.
Others cause the digestion of the various
complex sugars.

Digestive enzymes are made in other
animals and in plants as well as in man.
You can discover the effects of a plant
enzyme by doing Exercise 3. Man has
learned to extract some of the digestive
enzymes from living animal and plant
cells. In fact, some of them are extracted
in such large quantities that they can be
bottled and sold.

Not all enzymes are digestive enzymes.
Some make it possible for oxidation to
go on and there are manv others that are
necessary for the various cell activities.

Where digestive enzymes are made.
When the lining of the stomach or the
upper part of the small intestine is ex-
amined with a hand lens it is seen to be
dotted with pores. Each of these opens
into a microscopic bag or pocket sunk
into the wall of the digestive tube. In
the stomach alone there are approxi-
mately 35,000,000 of such pockets. The
pockets are lined by cells whose pro-
toplasm makes enzymes. We say the
protoplasm of these cells secretes (see-
creets') enzymes. When they are dis-
solved in water this mixture of water and
enzymes, together with some other sub-
stances secreted by the cells, is spoken
of as a digestive juice. As the digestive
juice diffuses out of the cells it fills the
bag or pocket. The juice then trickles out
through the pore into the stomach, or
small intestine, as the case may be. Such
a group of secreting cells is called a gland.
Those in the stomach are called gastric
glands. Those in the small intestine are
intestinal glands. It is interesting to note
that the glands of one part of your body
secrete certain products; those of another
part secrete different substances.

Large digestive glands outside the tube.
Digestive glands are not always micro-
scopic pockets like those just described.
Sometimes secreting cells are massed to-
gether, forming one large organ com-
posed of many microscopic "bags" or
"sacs." These tiny bags are clustered to-
gether much as the individual grapes
might be in a bunch of grapes. As the
cells of each bag secrete, the juice flows

192

through the little "stem" into the larger
stem. The large stem serves as a tube or
duct which carries the juice into some
part of the alimentary canal. Examples
of this type of gland organ are the three
pairs of salivary (saPi-very) glands, the
pancreas (pan'cree-as), and the liver.
Locate these organs on the diagram of
the digestive system, page 189.

The salivary glands empty their juice,
saliva, into the mouth. Some of the glands
open into the inside of the cheek; others
open under the tongue. The pancreas
lies behind the stomach, more or less
crosswise in the abdominal cavity. Its
juice, the pancreatic juice, enters the
small intestine close to the opening from
the stomach. The liver is by far the
largest gland of all; it lies above the

Houo a Complex Animal Uses Food unit iv

you can feel a smooth, moist membrane.
This delicate lining membrane is called
nnicous (mew'kus) membrane. It lines
not only the mouth but the whole alimen-
tary canal from beginning to end. The
membrane secretes a slimy, thickish sub-
stance called imicus. It is the mucus
which keeps the membrane smooth and
helps the easy passage of food.

Now provide yourself with a mirror
and some food. You can learn at first
hand how the mouth deals with food.
You can discover what the tongue does
in chewing and swallowing and in tast-
ing by doing Exercise 6. It will be worth
while also to make a study of the teeth
as suggested in Exercises 7, 8, 9, and 10.
The food an animal eats is often partially
determined by the kind of teeth it has.
stomach mostly on the right side. Under See Figure 203. Chewing is a purely me-

it and connected with it is a little storage
sac known as the gall bladder.

As the liver continues to secrete, the
juice known as gall or bile leaves the
liver and accumulates in the gall bladder.
After digestion is well under way the
gall bladder, which has thin muscular
walls, contracts slightly and releases the
bile. The juice flows along a duct which
joins the duct from the pancreas and
thus it reaches the alimentary canal.
While the liver, pancreas, and salivary
glands are not part of the alimentary
canal through which the food is pushed,
they are just as necessary to the whole
process of digestion as the canal itself.
This would be a good time for you to
dissect a frog to see the internal organs
in a freshly killed animal. See Exercises
4 and 5.

Food in the mouth. If you explore the
inside of your mouth with your fingers

chanical preparation of food for diges-
tion. Chewing breaks up food and mixes
it with saliva. Digestion begins when
saliva touches the food. Normally the
food remains in the mouth for so short
a time that not much of the starch can be
digested before the food is pushed on
toward the stomach. You can learn by
the simple experiment outlined in Exer-
cise 1 1 how long it takes for starch to be
changed into sugar in the mouth.

As soon as you begin to eat, juice flows
from the salivary glands very freely. The
presence of food in the mouth starts the
glands secreting actively. But the smell
and thought of food also is enough to
start their increased activity. Surely you
have seen a hungry^ dog watching the
preparation of its food. Why does it lick
its lips?

Food leaves the mouth. Although you
usually do not think about swallowing.

PROBLEM 2. The Digestive System Makes Food Usable

Fig. 203 How do you think
these various kinds of teeth
are associated with the dif-
ferent kinds of food eaten?

Toothless (Anfeafer)

Insect-eating [ArmadiiWo)

Herbivorous (Horse)

Meot-eoting (Dog)

Omnivorous (^tAan)

vou can swallow when you decide to
do so. But, once you have swallowed and
the food has entered the lower part of
the gullet you cannot control its pas-
sage. You can understand why this is
true when you learn more about the
muscles making up the walls of the di-
gestive tract. At the upper end are volun-
tary muscles. At the lower part of the
gullet and along the rest of the tract the
muscles are involuntary. You can control
voluntary muscles as you wish. Involun-
tary muscles are not under conscious con-
trol. They are, however, controlled by
other parts of the nervous system; they
need messages sent to them before they
contract or relax.

Figures 157 and 159 show that the cells
of voluntary and involuntary muscles are
quite different in appearance. The volun-
tary muscles are often spoken of as
striped, or striated (stry'ay-ted), muscles;
the involuntary are said to be smooth.
What other important difference is there
in the appearance of these two kinds of
muscles?

The various muscle fibers which make
up the walls of the food pipe lie in rings.
One ring contracts after another, thus
producing what seems to be a wave run-
ning along the tube. The wave is slow
but steady. If you have ever watched
a worm crawling, you will know how
the contracting food pipe looks, for the
same thing happens in the worm's whole
body. This wave of muscular contraction
is called peristalsis (perr-i-stall'sis). The
food is caught in this wave of contraction
and forced onward toward the stomach.
You will hear about peristalsis again in
connection with the intestines.

Digestion in the stomach. If you could
look at the inside of your stomach with
a magnifying glass at the moment the
food arrives there, you would see gastric
juice trickling from the microscopic gas-
tric glands through the microscopic
pores. And if you are enjoying the sight
and smell and taste of your food, you
would see the juice flowing even more
freely. One of our first American sur-
geons, William Beaumont, in the early

194

How a

part of the last century was fortunate
enough to see all this happening in a
human stomach. At an army post in
Michigan a trapper, Alexis St. Martin,
was shot through the stomach. It was a
large wound, right through the wall of
the stomach, large enough to put a fist
into. The man recovered but the hole
never completely closed and there was
left an opening through the body wall
between the ribs into the stomach. The
hole was so large that Beaumont could
look into the stomach. He could pour
water through the opening or introduce
food. He could suspend food in the
stomach for a certain length of time and
then recover it; he could siphon out di-
gested foods; he could measure the con-
tents of the stomach and could test the
juice chemically. While Beaumont was
performing all these experiments St.
Martin made his living by chopping
trees.

Because the composition of gastric
juice is known, a rather good imitation
of it can be made in the laboratory. You
will be interested in trying the effect of
imitation gastric juice on the various
food substances. See Exercises 12, 13,
14, and 15.

Gastric juice, like salivary juice, is
largely water. In it are hydrochloric (hy-
dro-klor'ric) acid, and several enzymes.
One of the enzymes, pepsin, changes in-
soluble protein, a very large molecule,
into the somewhat smaller molecules of a
substance called peptone. Peptones are
intermediate products of digestion. They
cannot be used by the body, nor will they
diffuse through the walls of the intestine.
Another enzyme, remiin, curdles milk
and helps in its later digestion. The third,

Complex Animal Uses Food unit iv

a fat-splitting enzyme, is of very little
importance in an adult. The hydrochloric
acid is not an enzyme. But it is of great
importance in digestion in at least two
ways. Unless it is present, protein is not
digested by pepsin. And besides, hydro-
chloric acid reacts with a number of
insoluble minerals, calcium phosphate
among others, producing soluble min-
erals.

Scientists have long wondered why
gastric juice which digests proteins does
not also digest the cells of the stomach
since protoplasm is made up largely of
proteins. No satisfactory answer has been
found. Some protection to the lining of
the stomach is probably provided by the
mucus secreted in large amounts by some
of the hning cells. This mucus spreads
itself over the inside of the stomach.

(Optional) Tissues making up the stom-
ach. The organs of the digestive tube are
complex organs composed of a variety
of tissues. You will find it helpful at
this point to review the section on tis-
sues in Problem 3 of Unit II. On the
outside of the stomach is a form of
epithelium, serous membrane. This thin
and very smooth, moist epithelial tissue
covers all the internal organs and lines
the body cavity. As the organs slide over
each other or against the inside of the
cavity there is little friction. The serous
membrane covers three distinct layers of
involuntary muscle. In one layer the
muscle fibers run lengthwise, in another
they are arranged in a circular fashion
around the stomach, and in the third
they are diagonal. In between these mus-
cle fibers there are fibers of connective
tissue which are always found in con-
junction with muscle cells. Lining the

PROBLEM 2

Fig. 204 The stomach and
the upper end of the small
intestine. Note especially the
mucous lining and the mus-
cle layers in the stomach.
How do bile and pancreatic
juice get into the intestine?

The Digestive System Makes Food Usable

Oesophagus ^,-
Pancreatic ducts
Bile duct

195

Gall bl

omall
intestine

Opening
of bile and
pancreatic ducts

Stomach there is a different epithehal tis-
sue called mucous membrane. This con-
sists of several layers of epithelial cells
laid on a foundation of connective tissue.
The epithelial cells secrete mucus. When
a large amount of mucus has accumulated
each cell is shaped like a flask and for
this reason these cells are called goblet
cells. Finally the cell bursts and the mu-
cus is discharged. Figure 228 on page
227 shows two goblet cells discharging.
Scattered through this mucous layer are
the microscopic glands that secrete gas-
tric juice. These are sunk into the thick
wall of the stomach. These glands are
made of epithelial cells of various kinds.
Blood vessels and the fibers of nerve cells
run through and between all these many
kinds of tissues. Thus, in this one organ
are found examples of all the different
kinds of animal tissues except bone and
cartilage.

Stomach movements. When the food
reaches the stomach much of it is still
in large pieces even if it has been well
chewed. During the two to four hours
that the food mass remains in the stomach
it is moved back and forth and around.

Oblique
Circular
Longitudinal

Stomach

,, ,. . muscle fibers

Mucous Immg

As the sets of muscles contract and relax
in turn, the stomach goes through several
kinds of movements but only some of
these movements are of the type that
move the food onward. The churning
movements break up the pieces of food
still further and mix them thoroughly
with the gastric juice. The importance of
these regular muscular contractions is
now recognized. Many of our digestive
disorders are the result of the improper
action of the muscular walls. By doing
Exercise 16, you can demonstrate the
importance of the mechanical breaking
up of food.

While stomach movements and diges-
tion continue, the rings of muscle at each
end of the stomach are more or less
contracted. Only liquids can pass through
the ring into the small intestine. What-
ever liquid food you eat passes on al-
most immediately after its arrival in the
stomach. After a while when digestion
has been going on for some time a ring
of muscle (the pyloric sphincter) be-
tween the stomach and intestine relaxes
more. As the softened and well-broken-
up portions of food are pushed forward

196 How a Complex Animal Uses Food unit iv

by peristalsis they are forced through intermediate products. If you wish to
the opening, a small amount at a time, know the details and the names of en-
After several hours the last of the meal zymes they are as follows: the enzymes
will have been delivered to the small in- which split fats are Upases — ly'paces.
testine. The stomach is empty and ready They change fats into fatty acids and
to receive more food when the next glycerin. The starch is converted by a
mealtime comes. It is important to know starch-splitting enzyme called amylase
that fats slow up secretion of juices and — am'i-lace — into a complex sugar which

muscle contraction; a meal rich in fats,
therefore, will remain in the stomach for
a longer time.

Food in the small intestine. Let us take
stock of what changes have occurred
when the food has reached the small in-
testine. A good many of the minerals
have been made soluble by hydrochloric
acid in the stomach. A very little of the
starch has been changed into a complex
sugar by saliva in the mouth. Most of
the sugars are just as they were when
eaten. Some of the proteins have been
split up into peptones by pepsin in the
stomach. Fats have, probably, scarcely
been touched. Much of the food has not
been acted on at all; some has been par-
tially changed but it is not yet completely
split up into compounds simple enough
to be used.

Having taken stock of what happened
before food arrives in the small intestine,
let us trace the food further. In the first
part of the small intestine the food comes
in contact with pancreatic juice, intes-
tinal juice, and bile. Let us note the effect
of each of these in turn. The pancreatic
juice has three types of enzymes: one
kind acts on proteins, one on starch, and
one on fats. The fats are changed by fat-
splitting enzymes into end products. The
starch is converted into complex sugar,
an intermediate product. Proteins, even
peptones, are changed into still simpler

is still an intermediate product, not the
kind of sugar a cell can use. Proteins and
peptones which had been formed in the
stomach are changed into intermediate
products even smaller than peptones, but
still intermediate products. (One of the
enzymes in the pancreatic juice that does
this is tryps'm — tv\^' sin.)

You can see that pancreatic juice does
not complete the job of digestion. Much
of the food is still insoluble. The intes-
tinal juice which works in partnership
with the pancreatic juice completes di-
gestion. Sunk into the walls of the small
intestine are microscopic glands like gas-
tric glands; these secrete intestinal juice
which contains three kinds of enzymes.
One kind (erepsin) makes amino acids,
which are end products, out of the pro-
tein intermediate products. Another kind
breaks down complex sugars into the
end product, glucose or other simple
sugar. The third acts on the fats not yet
digested by the pancreatic juice. Thus,
while the food is in the small intestine it
can be completely broken down into end
products that can find their way throuq-h
the intestinal walls and into the blood.

The bile from the liver contains no
enzymes but it aids in preparing fats for
digestion and it is important in various
other ways.

Preparation of fats for digestion. When
fats are warmed by the heat of the body

PROBLEM 2. The Digestive System Makes Food Usable

197

;;j^^;StarGK^;i;V^•

Protein

Complex

|||sugar!||||

Insoluble
minerals

Cellulose^

+ ptyalin or

+ pancreatic

enzyme

+ pepsin or

+ pancreatic

enzyme

(trypsin)

+ intestinal

enzyme

+ pancreatic
enzyme

IlilUIUIIMJIIll

.Complex

II [IP PI H-^. I M I

III sugar

+ intestinal

enzyme
(invertase)

Glucose

4^Peptones ,

/V/A/.'/y/.-/,/:'./..

+ intestinal
enzyme
(erepsin)

Amino acids

+ pancreatic
enzyme
(lipase)

+ hydrochloric
acid

Glucose or

other simple

sugar

Fatty acids
and glycerin

Soluble
minerals

^Cellulose

Fig. 205 This chart shows what happens to the principal jood' compounds in the ali-
mentary canal. Which are intermediate products and end products of digestio?i?

they turn into liquids; that is, they be-
come oils. Sometimes you eat fat already
in a liquid form as when you eat olive
oil. When an oil is mixed with water it
soon separates from the water so that a
few large drops are formed. Enzymes
cannot act quickly on such large drops
of oil because they can act only at the
surface. The oil must be broken up into

juice is made active (activated) by the
salts. Without this activation the enzyme
does not digest fats.

Absorption of digested food. You have
learned that in digestion large molecules
are broken up step by step into much
smaller ones. Proteins are changed into
amino acids, fats into fatty acids and glyc-
erin, and starches and sugars into simple

little droplets before much digestion can sugars (such as grape sugar or glucose).

go on.

When bile is thoroughly mixed with
an oil it forms a thin film around each
droplet of oil so that the droplets can no
longer come together. When oil has been
broken up into tiny droplets in this way
it looks milky. It is in a state of emiilsio7i
(ee-mul'shun). Milk is a good example
of an emulsion. The fat in milk is in very
tiny globules. You can easily make an
emulsion in a test tube by doing Exer-
cise 17. Could you demonstrate the prin-
ciple that by emulsifying fats you
increase the digestive surface? See Ex-
ercise 18.

The bile salts help in another way. The
fat-digesting enzyme of the pancreatic

Insoluble minerals are made soluble. As
these end products of digestion are pro-
duced they may begin to diffuse through
the walls of the alimentary canal into the
blood. This movement through the walls
into the blood is called absorption.
Wherever there are digested foods ly-
ing close to the lining of the digestive
tract for any length of time some ab-
sorption takes place. But there is little
absorption until the food reaches the
small intestine. While food is still in the
stomach not much of it is ready for ab-
sorption, nor does it have an opportunity
to stay in close contact with the mucous
membrane since the stomach is a large
pouch instead of a narrow tube.

198

Honjo a Co?nplex A?iimal Uses Food unit iv

Absorption is more than simple diffu-
sion through a Hfeless membrane. The
cells that absorb take an active part in
the absorption as is shown by the fact
that they use more oxygen and produce
more carbon dioxide while they are ab-
sorbing.

Absorption by the small intestine. If
you were to slit open the small intestine
along its length and examine the inside
with a powerful magnifying glass, you
would find it moist and pink like the
lining of your cheeks. But in other re-
spects it would be different. The inside
of your mouth is smooth; the lining of
the small intestine is wrinkled into deep
folds, sometimes one third of an inch
deep. If you rubbed your hand over the
folds and if your sense of touch were
delicate enough you would discover that
the folds feel like a soft brush or like
plush, for they are covered with micro-
scopic, hairlike projections. These are
called villi (vilPeye), plural of villus.
They are soft because they are made of
delicate cells. They sway back and forth,
now lengthening, now shortening. They
and the folds increase the lining surface
enormously. It has been estimated that
the surface of this narrow tube is more
than five times as great as the skin sur-
face of your whole body. Study the
drawing of a villus (Fig. 206) to see how
the digested foods can diffuse through
the thin layer of mucous membrane cov-
ering the villus and go into the tiny
blood vessels just underneath. Once the
food is in the blood vessels it can be car-
ried to larger and larger vessels and sent
to every part of the body. In the center
of the villus is a lacteal (lack'tee-al) into
which the fatty acids and glycerin go.

Capillaries

Lacteal {lymphatic)

Mucous membrane

Muscle cells

Vein Artery

Fig. 206 One of the villi of the sjnall intestine
cut through lengthwise. How many kinds of
tnbes does the villus contain? Can you see the
opening of one intestinal gland alongside the
villus?

These products of fat digestion reach the
blood stream later.

The large intestine. Parts of our food
are never digested because we have no
enzymes to act on them. This is true of
the thick cellulose walls of plant cells,
known as roughage, and other portions
of our food. These substances that have
not been digested are pushed on into
the large intestine. Here much water is
absorbed and the residue is ejected, or
eliminated, throuoh the anus. But the
nondigestible foods have actualh" been
useful. While in the small and large in-
testines they stimulated the walls to con-
tract, helping peristalsis.

How does the liver function? You have
read how the bile helps in emulsifying
oils. It is of even greater importance in

PROBLEM 2. The Digestive System

the absorption of fats. But the Hver is
helpful in still other ways. Besides con-
taining gland cells which make bile it
has ordinary cells which serve as a store-
house of carbohydrates. You have read
that the end product of carbohydrate
digestion is a simple sugar, mostly glu-
cose. This is the kind of su^ar that the
cells of the body can use. However, the
blood cannot hold more than a small
amount of glucose at one time. Under
normal conditions, much of the suaar
that is absorbed into the blood leaves the
blood stream in the liver. Here it is
changed into an insoluble material similar
to the starch found in a plant. This in-
soluble substance is called glycogen (gly'-
ko-jen). Converting glucose into gly-
cogen is the opposite of digestion. An
enzyme brings about the change. Later,
as the amount of sugar in the blood de-
creases, the glycogen is changed back
into glucose and diffuses into the blood.
In this way the sugar concentration in
the blood is kept almost constant.

The liver functions in another way.
It changes certain amino acids which
would otherwise be wasted into a useful
substance, glucose. On page 190 amino
acids were compared to "building stones"
as parts of protein molecules. When you
eat protein and eventually build up your
own bod\^ protein, it is much as though
you wrecked a number of houses and
then used some parts of one and other
parts of another to build your own new
house. Your new house has a special de-
sign which makes it impossible for you
to use all the parts of the house or houses
you wrecked. So when you eat and di-
gest (wreck) proteins from various ani-
mals and plants you get "building stones"

Makes Food Usable

199

(amino acids) of different kinds. You
can use some for assimilation; the others
are changed in the liver into two sub-
stances. One is a nitrogen compound
called urea, a waste product. The other
is glucose which can either be oxidized
immediately or stored as glycogen.

What stirs the glands to action? Secre-
tion in the glands must be well timed, or
much digestive juice will be wasted. You
have already read how the sight and
smell or even thought of food sends mes-
sages along the nerves to the salivary
glands and the gastric glands which then
begin to secrete actively. This goes on
without your thinking about it or know-
ing what goes on inside of you. The mere
presence of food against the mucous lin-
ing also stirs these glands to action.

But digestive glands may be made to
secrete actively in still another way. At
the beginning of this century two Eng-
lish scientists performed a very interest-
ing and important experiment. They had
been led to believe that there were sub-
stances in the blood which stimulated
the pancreas to secrete. To test their
theory the following experiment was
performed. Two dogs were operated
upon and a large blood vessel of one dog
was joined to the corresponding blood
vessel of the second dog. In this way the
blood of each dog flowed through the
body of the other. Then one animal was
fed and the other was left unfed. After
some time, when the digested food ar-
rived in the small intestine of the dog,
there was a flow of juices in both dogs!
Since the only connection between the
two dogs was their blood vessels it
seemed as though something to stimulate
the pancreas must have been carried by

2 00 Houo a Complex Animal Uses Food unit iv

the bloodstream from dog to dog. This also be partly responsible for the stimula-
experiment and similar ones were re- tion of the intestinal glands. Secretin is
peated, always with the same results. For one of many "chemical messengers" in
this reason the experimenters concluded the body. Such substances that are ear-
that there is a substance carried by the ried in the blood and act as chemical
blood which stimulates the pancreas; they messengers are called homiones. There is
called it secretin (see-cree'tin). believed to be a different hormone which
Secretin gets into the blood from the stimulates the liver and perhaps another
mucous membrane of the small intestine, for the gastric glands.
When the first food materials from the The action of digestive glands can be
stomach arrive in the small intestine, slowed up as well as increased. Dr. Wal-
they stimulate some mucous membrane ter B. Cannon of Harvard University has
cells to form secretin. The secretin enters demonstrated that anger or other excite-
the blood. It circulates with the blood ment interferes seriously with the secre-
and promptly reaches the pancreas. tion of gastric juice in a cat. You can
When it arrives there it causes that gland read an account of his experiments in his
to secrete very actively. Secretin may book, The Wisdoin of the Body.

Questions

1. Name in order the parts of the digestive tube or alimentary canal.
How long is it? How long does it take food to pass from end to end?

2. Where in the body is food constantly needed? If it is carried by the
blood, explain through what it must pass to get into the blood.
Which substances can diffuse through the walls of the digestive tube
and blood vessels? Which cannot?

3. What is meant by digestion? Why is this called a chemical change?

4. Explain intermediate and end products of digestion. Give examples.
How does the number of amino acids compare with the number of
different proteins?

5. What is the result of adding saliva to cooked starch? What kind of
substance in saliva changes starch to sugar? What is the name of this
substance?

6. Define catalyst. How do enzymes differ from other catalysts? In
which cell activities do enzymes help?

7. What is the work of a gland? Define the word secrete. Describe a
microscopic gland and name two kinds of microscopic glands that
help in digestion.

8. Name tlirce gland organs that lie outside the digestive tube and that
help in digestion. How do they differ from gastric glands? How does
the gall bladder function?

9. State four ways in which the tongue functions. Describe the lining
of the mouth and the whole digestive tube. Name three substances
making up a tooth. What starts the secretion of the salivary glands?

PROBLEM 2. The Digestive System Makes Food Usable 201

10. Why are the muscles of the digestive tube beyond the throat called
involuntary muscles? Distinguish between voluntary and involuntary
muscles in appearance. What is the other name for voluntary mus-
cles; for involuntary muscles? Describe peristalsis.

11. What starts the secretion of the gastric glands? Of what is gastric
juice composed? What is the importance of each substance?

12. Name and describe the tissues which are found in the wall of the
stomach. Which important tissues are not found?

13. Describe the muscles in the walls of the stomach and tell how they
function. How does food get into the small intestine?

14. Sum up the changes that have taken place in food by the time it
reaches the small intestine. Name three juices it meets there. Explain
the changes brought about by pancreatic juice in three kinds of food.
Explain how intestinal juice completes the work of the pancreatic
juice.

15. Is emulsification a physical or a chemical change? Explain. How does
emulsification help? In what two ways is the bile of help in digestion?

16. Why is there little absorption of food in the stomach?

17. The small intestine is long and narrow; it has folds; it has villi. Explain
how each of these structures is useful in digestion or absorption.

18. Normally, which parts of our food reach the large intestine?

19. What is glycogen? Explain its relation to the liver. In what sense

are amino acids building stones? How does the liver put amino acids
to good use?

20. Where is secretin made? How does it function? Why is secretin called
a hormone? Explain three means by which digestive glands can be
stirred to action. How is the secreting of the digestive glands some-
times stopped?

Exercises

1. Can starch enter an artificial cell? Prepare an artificial cell by filling
a gelatin capsule with some white of t^^ and sugar solution. Make a thin
starch paste by heating a small amount of starch in a large amount of
water. Cool. Place the capsule in the paste. After two hours remove the
capsule and test the contents for starch. What test will you use? What
do you observe? What conclusions can you draw about the entrance of
starch into the cell?

2. Does saliva change starch into sugar? Prepare a solution of boiled
starch. Pour some into each of two test tubes. Add saliva to one test tube
and let it stand in a warm place for half an hour or more. Now test part
of the solution in each of the test tubes for sugar. (Use Benedict's or Feh-
Ung's solution.) Test another part for starch. Before you draw a conclu-
sion make sure that you have eliminated every other possible conclusion.
What else must you do?

202 ^ How a Co?nplex Animal Uses Food unit iv

3. Do active plant cells digest starch? The cells of a dried grain of corn
are living but quite inactive. They will become active when the grain
is soaked; it will then sprout. Soak grains for 24 hours. Keep them moist.
After 4 or 5 days test dry and sprouted grains for sugar and starch. What
do you notice? Be sure to keep accurate notes. How can you explain what
happens? Did you use a control? What was it?

4. Ho'iv to dissect a frog. Lay a dead frog in a shallow pan with ventral
(lower) side up. With your forceps grasp the loose body wall in the ex-
treme lower part of the body cavity where the legs arise. Cut into this
body wall with the point of your scissors making a large enough incision
for you to introduce the point of one blade. Now remove the body wall,
cutting out a complete rectangle. Caution: As you cut, the scissors must
be held horizontally and with the forceps you must raise the body wall in
front of the scissors. In this way you will not damage the organs within.
Cut from the point of incision to your right (the frog's left) across the
lower portion, then up along the side until you reach the head. In the
region of the arms you will be obliged to cut through the bones which
make the shoulder girdle. Then cut the third side of the rectangle and
back along the left (the frog's right) side. When you have removed this
large piece of body wall the internal organs of the frog will be exposed.

5. Study of the internal organs. During the breeding season the female
frog will have large masses of eggs. These must be removed before you
can see the other organs. The heart may attract your attention since it
may be beating. In the region of the heart toward the front end of the
body cavity are the large, flat, dark red lobes of the liver. How many are
there? Attached to the liver you will find the gall bladder which is green.
What is its shape? Partly under the liver on the frog's left side is the
long, whitish tubular stomach. Feel it with the dull point of the forceps.
How does it feel? At its lower end it narrows to form the tubular intes-
tine. Trace the coils of the intestine. You will find that it is held down
and held in place by a very thin membrane called the mesentery. Do you
see fine blood vessels in the mesentery leading to the intestinal wall? The
small intestine widens into the large intestine. Caught in the folds of the
mesentery in the region of the stomach is the long narrow pancreas.

Other organs you will see are: the spleen, a dark red ball; lying against
the back wall in the region of the heart, two narrow pointed pinkish
lavender bags, the lungs; against the back wall two dark red, rectangular
organs close together, the kidneys; close to the kidneys, perhaps, a pair of
yellow organs if you are studying a male frog, the male reproductive
organs. Try to inflate the lungs by inserting a tube through the frog's
mouth and blowing into it.

6. Study your tongue with a hand mirror. Where and how is your
tongue attached? Which parts of your mouth can be touched by your
tongue? When would these movements of the tongue be of help to you?
Explain. Put a drop of sugar water on the front of your tongue; on the

PROBLEM 2. The Digestive System Makes Food Usable

203

Fig. 207 Longitudinal section of an in-
cisor. The different kinds of teeth all
have the same three regions. What are
they? All are alike in structure.

Ename

' Crown

Neck

Dentine

Cement

Nerve and
blood vessels
to dental pulp

Root

back. Do you note any difference? Now put a grain or two of granulated
sugar on your dry tongue. What do you discover.^ Blindfolded, and with
nose tightly shut, taste the following substances (someone must put them
on your tongue without telling you which is which): salt, lemon juice,
vinegar, sugar, something bitter, grains of ground coffee, farina, etc.
Rinse your mouth after tasting each substance. Which can you recognize?
Repeat, with your nose no longer held shut but still blindfolded. What do
you conclude? All of your observations must be carefully recorded.
Compare them with your classmates'. Why? Can you now name four
different ways in which the tongue functions?

7. What can you discover about the number and the arrangement of
your teeth? It will help you in your study to know that the teeth in the
upper and lower jaws are alike. Use a mirror to discover how you bite
off a piece of bread. Which teeth do the work? How are they fitted for
it? You have four such teeth at the front, in each jaw. They are called
incisors. Which group of mammals has the incisors well developed? Right
behind the incisors, you have a single tooth on each side which is some-
what more pointed. It is a cuTime, the tooth which is so large in cats, dogs,
and their relatives. How do the back teeth differ in shape from incisors
and canines? How many back teeth are there in each jaw? How do they
function? Bite into a piece of hard chewing gum. What impression does
each kind of tooth make on the gum? Can you see that the two teeth
directly behind the canine differ from those still farther back? How?
Those farthest back are the molars. Between the molars and the canine lie
the bicuspids. If you have your last molars, called wisdom teeth, and
have lost no teeth, you can count 32 teeth in all. How many have you?
Write a report of your observations.

2 04 - How a Complex Am?nal Uses Food unit iv

8. How are the teeth fitted for their work? How does the surface of
your tooth differ in appearance and in structure from the surface of a
bone? Your tooth is covered with a substance much harder than bone.
It is called enamel. Study the diagram of the tooth. Where does the enamel
end? Explain. Dentine is a substance much like bone. Like bone it con-
tains cells. But enamel is pure mineral matter. What is found in the very
inside of the tooth? Which are the living and which the lifeless parts of
the tooth? When you have a toothache, you feel pain through the nerve.
Where does the nerve lie? What has probably happened to make the
tooth ache? What might cause a toothache while you were eating?

9. What can you do to make sure that your teeth are covered with a
good layer of enamel? Write a paragraph on the connection between
good teeth and diet. (See Problem i of this unit.) Since enamel is pure
mineral matter it is not only hard but brittle. What might tend to crack
it? Ask your teacher to do the following: Put into a test tube a small
amount of calcium phosphate (the mineral that makes up enamel). Shake
it well with a little water. Examine. Add some strong hydrochloric acid.
What do you observe? Add weak acid to a very small amount of calcium
phosphate and let it stand. What conclusions do you draw? When bac-
teria decay food they often form acids. If small particles of food left in
your mouth decay, what might happen?

10. You will find it interesting to make a list of all the rules you can
think of which would help to keep your teeth in good condition. Of
course, unless you can give a good reason for your rule no one will be
interested in it.

11. How quickly does saliva act in the mouth? Grind up a small piece
of soda cracker and moisten it. Lay it on your tongue. Look at the clock.
What do you taste? Leave it there several minutes. What do you notice?
Explain. Did other members of the class get similar results or is this a
peculiarity of your saliva?

12. What is the effect of gastric (stomach) juice on starch? Ask your
teacher to make some artificial gastric juice by adding to a test tube of
water a few drops of hydrochloric acid and a little powdered pepsin.
Add some of this to starch in a clean test tube. What happens? State
clearly what you did to arrive at a conclusion. What was the control?
State your conclusion.

13. What is the effect of gastric juice on protein? Cut some hard boiled
white of &^^ into small pieces. Put a quarter of a teaspoonful into a test
tube, add two inches of artificial gastric juice, and plug the tube with
cotton. (The experiment will be more successful if you boil the \\'ater
and take all precautions to exclude bacteria.) Keep the test tube in a warm
place. Why? What temperature would you suggest? What would you
suggest as a control for this experiment? Examine it alter 10 minutes,
several hours, 24 hours, and 48 hours. Make a note of any changes you
observe. Explain what you see.

PROBLEM 2. The Digestive System Makes Food Usable 20^

14. What in the gastric juice digests protein? x\re you convinced that
it was the pepsin that digested the white of t^g? Can you prove that it
was not the water? Or the hydrochloric acid? Try each of the three sub-
stances alone. What happens? Now plan an experiment to discover what
is really necessary for the digestion of protein. Include in your report of
this experiment a statement of the control experiments that were used.
Tell why they were necessary.

15. What is the effect of hydrochloric acid on the minerals in the food?
Test such minerals as table salt and calcium phosphate. Use dilute acid
and very small amounts of mineral. Describe what happens.

16. How does the mechanical breaking up of food affect digestion in
the stomach? Can you devise an experiment to answ^er this question?
(Hint: Use hard boiled white of to^g and gastric juice. Use two tubes.
How must the white of t^^ in the two tubes differ when you set up the
experiment? )

17. How can oil be emulsified? Place about one-half teaspoonful of
olive oil in a test tube half filled with water. Shake the contents and allow
to stand for several minutes. What happens? If it is possible to obtain
the gall bladder of a chicken, add this bile to the oil and water in the test
tube. If not, use a weak alkaline solution obtained in the laboratory. Hold
your thumb over the mouth of the test tube and shake the tube thor-
oughly. You now have an emulsion. What is its color? Examine after
several minutes. Does the oil again rise to the top? Examine a drop of the
emulsion under low power of the microscope. What do you see? Can you
explain the emulsion? Explain how emulsification prepares oils for diges-
tion.

18. Does emulsification appreciably increase the surface to be acted on
by digestive juices? Fasten together several board erasers or books with
an elastic. Measure their total surface area. Separate them and measure
the surface of each one. Add together the measurements of the separate
objects. Compare this sum with your first measurement. Can you ex-
plain? A cube whose side is one inch has a total surface area of six square
inches. If this cube is cut up into small cubes whose sides measure 0.0 1 of
an inch there will be one million such cubes. What will be the total sur-
face area of all of the small cubes? How does it compare with the area of

the original cube?

Further Activities in Biology

1. Devise an experiment to determine whether the enzyme in saliva
really acts like a catalyst; that is, whether a small amount can be used over
and over again without being used up in the process.

2. If saliva is swallowed with starch, can its work continue after it
reaches the stomach? You must expose saliva and starch in a test tube to
the surroundings they would have in the stomach. What will you do? Ask
to have your experiment tried in class.

PROBLEM 3 How Are Materials Moved to and from

Our Body Cells?

The transportation system. You have
learned that in the human ahmentary
canal there is large scale digestion of
food and that digestion produces mate-
rials that may be assimilated or oxidized
in the cells. But there are bilhons of cells
in the body, most of them far removed
from the alimentary canal where diges-
tion takes place. Digested foods are trans-
ported to the cells by a transportation
system called the circulatory systeju.
There are really two systems. One sys-
tem is composed of the heart and blood
vessels through which blood moves. The
other consists of tubes called lymphatics
which carry lymph. Let us study the cir-
culation of the blood first.

Blood circulates in a system of two
connected sets of tubes. It is pumped to
all parts of the body by the heart through
one set, the arteries. It flows back to the
heart through another set, the veins.

How food enters the blood system. Di-
gested foods in the small intestine are
absorbed by the villi. Each villus contains
tubes of two kinds. There is a network
of tiny blood vessels which are part of
the blood system; and there are tubes
called lacteals which are part of the
lymphatic system. The blood vessels in
the villi are microscopic with very thin
walls. Such tiny blood vessels with ex-

tremely thin walls are known as capilla-
ries (cap'ill-a-rees). Digested foods easily
enter them and become part of the blood.

Capillaries in all organs. Just as there
is a small network of capillaries in the
villi, there are netM'orks of capillaries in
every organ, such as the brain, the in-
ternal organs, the muscles of the whole
body, and the skin. You cannot see these
capillaries in your body because they are
microscopic but by doing Exercise i
you can get a very good idea of how
they must look. They are so tiny and
branch so widely that they are spread
through every part of the body. Every
cell is more or less closely in contact
with capillaries.

The digested foods diffuse out through
these capillaries which lie among all the
cells of the body; thus the food sub-
stances reach the living cells. Every or-
dinary cell engages in many activities,
but the activities are on so small a scale
that you are not aware of what is going
on. One of these activities is oxidation.
Not only food but oxygen as well dif-
fuses out of the capillaries into the neigh-
boring cells. As a result of oxidation,
energy is released and new substances are
fonned. Some of these are harmful to
protoplasm; at best, they are useless.
They are the waste products. The wastes

PROBLEM 3. How Materials Are Moved to and jrom Cells

207

Fig. 208 Part of the web of a frog's foot ?nag-
nified 75 tiines. The irregular dark spots are
coloring matter in the skin. The very faint, nar-
row vessels are capillaries. What are the wider
vessels? In what ways is the blood chatiged
while it is in the capillaries? (hugh spencer)

formed in oxidation diffuse through the
capillary wall into the blood. As you
continue to learn how the human body
performs its life activities you will dis-
cover that there are still other substances
which enter and leave the thin-walled
capillaries in all the organs of the body.
Long distance transportation to and
from the organs. The tiny, thin-walled
capillaries connect the longer and wider
arteries and veins. Transportation from
one region to another is through the
wider tubes. The walls of arteries and
veins are much thicker than the walls of
capillaries. Blood flows through arteries
and veins over long distances to and from
the organs. Within each organ the artery
branches into smaller and smaller arteries.
The smallest of these arteries connect
with capillaries within the organ. The

Heart

Fig. 209 The heart and some of the large veins
(dark) and arteries (light) of the main circida-
tory system. The heart is the organ which
pimips the blood to all parts of the body
through the arteries. The blood flows back to
the heart through the veins. Connectijig the ar-
teries and veins are the capillaries (see Fig. 208).
Every cell in the body lies near one of these
microscopic tubes. How are digested foods and
oxygen obtained by the living cells, and how
are waste products carried away? The ly?ft-
phatic system is not shown in this diagram.

208

capillaries, in turn, are joined to small
veins. More and more veins join, forming
larger veins through which the blood
flows away from the organ.

Substances are transported through the
arteries and veins very rapidly. Within a
few minutes drugs absorbed by the di-
gestive system or gases breathed into the
lungs can be found in any organ of the
body.

What is blood? Blood consists chiefly
of an almost colorless, slightly straw-
colored liquid, called plasrim. Plasma is
about 90 per cent water. In it are dis-
solved the digested foods which have
been absorbed in the small intestine and
the various wastes which are constantly
being added from the working cells.
Plasma also contains various types of pro-
teins which are of great importance in a
number of ways. One of them, for in-
stance, helps in blood clotting. It is called
fibrinogen (fye-brin'o-jen). Besides all
these substances, plasma contains hor-
mones (one hormone, secretin, was dis-
cussed on page 200), and it carries
substances which help us fight disease.

You can see that plasma is not a simple
substance. The make-up of plasma is not
always the same; plasma is constantly
changing. If the cells in some part of the
body are carrying on oxidation at a rapid
rate, wastes will be added to the plasma
in large amounts. During sleep the
amount of waste material present in the
transportation system is less. Some hours
after a large meal, when the digestion of
food is well on its way, the plasma will
contain large amounts of substances pro-
duced by digestion. If the meal was
largely beefsteak the plasma will be rich

How a Complex Animal Uses Food unit iv

Platelets

Nongranular
cell body

Nucleus

White corpuscles

Fig. 210 Three kinds of blood cells. How do
these cells differ in size and shape? ^Vhat part
usually found in a cell is inissing in the red
corpuscles? Of what use is each kind of cell?

in amino acids which come from protein
digestion. If the meal was largely starches
and sweets the plasma will contain more
sugars. When you are exercising, the
absorbed food substances are rapidly
enteriniT the working cells. You have
seen the loading and unloading of a bag-
"■auc car at a station. The contents of the
car change at every stop; just so with the
plasma. Only the blood does not have to

PROBLEM 3. How Materials Are Moved to and from Cells

stop in its course to load and unload. As
it moves through the capillaries there is
a constant passage of substances in and
out.

Blood is more than just plasma. In the
plasma there are three kinds of cells: red
corpuscles (core''pus-ls), white corpus-
cles, and tiny platelets (plate'lets). The
red corpuscles are very numerous and
give the red color to the blood. If you
follow directions in Exercise 2 you can
study a drop of blood with a microscope
and see the two kinds of corpuscles.

Almost half of the volume of the blood
is cells. For this reason blood is thought
of as a tissue. Some of the other tissues
which you think of as "solid" tissues have
almost as much liquid around their cells.
If your school has an instrument known
as a centrifuge (sen'tre-fewj) you can
easily separate the blood plasma from
the mass of cells. If you can get blood
from a slaughter house, do Exercise 3.

Red corpuscles. A red corpuscle is
shaped like a coin which is much thinner
in the center than around its edge. The
red corpuscles contain a special protein
substance, rich in iron, known as hemo-
globin (he^mo-globe'ln). Hemoglobin is
unlike other proteins in that it unites
with oxygen very easily and releases it
just as easily. It is because of this that
the red corpuscles can be the transport-
ers of oxygen. When hemoglobin unites
with oxygen it forms a new compound
(oxyhemoglobifi) which is bright red in
color. If, later, this red compound is in
surroundings where there is little oxygen,
it again separates into oxygen and hemo-
globin. When blood flows from a cut it
is at once exposed to oxygen and there-

209

fore takes on the color you think of a?
blood red. When examined under the
microscope, however, red corpuscles are
disappointing, for each single cell is quite
pale even when in contact with oxygen.
It is only when there are large numbers
of red corpuscles close together that we
can see the brilliant red color of fresh
blood.

Red corpuscles are much smaller than
most other body cells. One drop of blood
normally contains more than 5,000,000
of them. Since there are more than five
quarts of blood in the average man he has
about twenty-five trillion (25,000,000,-
000,000) red blood cells, a number too
large to hold any meaning for most of us.
It may mean more to learn that if all the
red corpuscles of a normal person, small
as they are, were laid out flat next to one
another they would cover an area as
large as a baseball diamond.

Red corpuscles are made in the red
marrow of the bones. Before they enter
the blood they lose their nuclei. They
live, on the average, only about a month.
In healthy people about a million cells
may be destroyed every second. If they
are destroyed too rapidly, or are not
manufactured fast enough, or if a large
amount of blood is lost, a person may
have too few red corpuscles. He then
has too little hemoglobin, a condition
called ajiemia (an-ee'me-a). Since iron is
an important part of hemoglobin, an in-
sufficient amount of iron in the diet can
also cause anemia. The organ known as
the spleen is a reservoir of blood and
particularly a storage chamber of red
corpuscles. During muscular exercise and
in people living at high altitudes the

2IO

How a Co?;iplex An'wial Uses Food unit iv

spleen contracts more vigorously than
usual and thus increases the number of
red cells in circulation. This is interesting
because in both cases it is an advantage
to the person to have more corpuscles.
When exercising he needs more oxygen.
At high altitudes there is less oxygen in
the air and a large number of corpuscles
is desirable.

White corpuscles. We have many kinds
of white corpuscles, or leucocytes (lew'-
ko-sites). Those that are most numerous
are large cells that resemble an ameba in
shape; that is, they have no definite shape,
since their soft protoplasm streams now
in one direction, now in another, form-
ing pseudopods. Their protoplasm is
quite granular and the nucleus is large
and usually shaped like an irregular club.
These white corpuscles move about much
as an ameba would. The great Russian
biologist Eli Metchnikoff (i 845-1 91 6)
discovered these cells near the end of the
last century and called them phagocytes
(fag'o-sites). They can push their way
between the cells that make up the walls
of the capillaries and get in among the
tissue cells. Here they engulf and grad-
ually digest bacteria or any other parti-
cles that are present. They serve as tiny
scavengers (eaters of unwanted sub-
stances) in the body. When bacteria
enter the body, millions of the phago-
cytes and some of the other kinds of
white cells are soon attracted to the spot.
The other kinds are helpful in surround-
ing this whole region and keeping it
separated from the neighboring tissues.
The large white corpuscles begin at once
to devour bacteria. As many as twenty
bacteria have been found within one
corpuscle. Often the white corpuscles

White cell fphagocyfej

Bacteria

Fig. 211 Three white cells (phagocytes) de-
stroying bacteria by engulfing and digesting
them. How is this activity of the white cells
of benefit to the body?

are killed by the poisons secreted by the
bacteria. The dead bodies of the white
corpuscles together with destroyed tis-
sues is pus. This whole region, or abscess
(ab'sess), is red, swollen, and hot to the
touch. Much blood is present.

Some kinds of white corpuscles are,
like the red corpuscles, made in the red
marrow of the bones. Other kinds of
white corpuscles are made elsewhere, in
what we call lymph glands. You will
read of this later.

Blood platelets and clotting. The third
kind of blood cell, the platelet (small
plate) is the smallest. It has no nucleus.
Platelets are connected in some way
with the clotting of the blood. You have
seen how the blood which oozes out of
a small cut hardens or clots. If it did not
clot and thus plug up the blood vessel,
the blood would keep right on flowing.

According to one theory of clotting,
the platelets together with other cells
start the process of clotting by breaking
up when the blood vessel is damaged.
As they break up they release a sub-
stance. This substance indirectly causes

substance

which
indirectly

acts on

form

_5:!^i£hentangj£

PROBLEM 3. Honjo Materials Are Moved to and jro?n Cells

one of the dissolved proteins of the K^jg|i^V^-
plasma, fibrinogen, to harden and form '^^^^:^f^^'^^&-^
threads. These are known as fibrin (fye"- —

brin) threads. They entangle the red and
white corpuscles, and this tangled mass
is the clot.

When a large quantity of blood is
allowed to stand in a tumbler a solid mass
of fibrin threads and corpuscles forms in
the way just described. This mass shrinks
and you then see it as a clot floating in
a faintly yellow liquid \\'hich looks like
plasma. But it is not plasma because it has
lost the fibrinogen which hardens into
threads. It is sermii, a substance which
does not clot. You may have heard that
a doctor sometimes injects purified blood
serum into a person.

In most people bleeding from small
wounds stops soon because of clotting.
Bleeding from larger wounds may often
be stopped by various methods used by
physicians. Sometimes vitamin K is in-
jected to hasten clotting. Some people
are known as "bleeders" because their
blood clots very slowly. The cause of
this condition is not definitely known.

Transfusions and blood banks. The
transfer of blood from one person into
the veins of another is practiced when
large amounts of blood have been lost, in
treating for shock, and under various
other circumstances. Great care must be
taken to choose the right person to give
blood. If the blood of the donor (the
person who gives) is not of the right
type it clots or coagulates within the
body of the patient, causing death. There
seem to be four main groups of people,
classified according to the chemical com-
position of their blood. This has nothing
to do with the race to which they belong

21 1

fibrinogen
a protein
in plasma

Fig. 212 Hoiv blood is supposed to clot. Begin
at the top. Cells, mostly platelets probably, start
the process. Of what is the clot composed?
What surrounds the clot?

because the same four groups are found
in all races. It was once thoutjht that one
type of person, called the universal
donor, could give blood with safety to
any other person. While in general this
"universal" blood, called also "O" blood,
can be mixed with any of the four types,
occasionally there are disastrous results.
For this reason tests are made before the
transfusion. A second type of blood is
"A" blood; this can be used only for a
person who also has "A" blood. A third
type called "B" blood can also be mixed
only with its kind. The fourth kind is
called "AB." The person with "AB"
blood can receive blood from every
other type and is called the "universal
recipient." Here again there are occa-
sional exceptions. This knowledge of the
four kinds of blood is the result of the

2 12

How a Cojnplex Ani?nal Uses Food unit iv

Fig. 213 This pJ:)otograph
was taken while the man was
donating blood for the third
time at a Red Cross Center
during World War 11. How
was the blood used? Is there
still a need for blood dona-
tions?

work of a great physiologist, Karl Land-
steiner, who died in 1943.

Also it was discovered recently that
there is a substance in the blood of most
people called the "Rh factor." A few
people lack it. The name comes from the
animal, the Rhesus monkey, used in the
experiments which led to the discovery
of the substance. If the mother lacks the
Rh factor, the development of the un-
born child may be interfered with; some-
times the child dies.

When transfusions were first given it
was necessary to introduce blood from
the donor directly into the patient. Since
the first World War, thanks to an im-
portant discovery made by a scientist in
Argentina, Dr. Luis Agote, we have
learned to preserve blood so that the red
cells do not die. Now blood can be col-
lected and kept in blood banks.

Using parts of the blood instead of
whole blood. At the present time plasma
and sometimes serum is used rather than

whole blood because neither plasma nor
serum need be matched. Besides this,
plasma has the great advantage that it
can be easily dried and readily preserved
without spoiling. With the addition of
distilled water dried plasma is ready for
use. In this kind of transfusion the
wounded receive no red blood cells but
this is often not as important as you
might think because ordinarily the body
has a large supply of these in reserve.
During World War II most of the blood
which was given through the Red Cross
was used to produce dried plasma.

Very recently chemists have gone one
step farther. They have learned to sep-
arate the proteins in plasma from each
other. Professor Edwin Cohn of Harvard
University has been a leader in this work.
It has been found, for example, that not
the whole plasma but only one of its
proteins is needed for treating shock.
This one protein when separated from
the rest will occupy far less space and

PROBLEM 3.

Superior

vena

cava

Hoiv Materials Are Moved to and from Cells

Aorta Right aurick

Pulmonary
artery

Right and left Veins
ventricles

Right ventric

Fig. 215 (above) The heart cut open. Note
the four chambers. From which chambers and
through which tubes does blood leave?

Fig. 214 (left) The heart. This is the pump
that keeps the blood in constant motion.

be easier to carry; and the other proteins
can be used for other purposes.

The blood is in constant motion. The
plasma with its blood cells travels to the
farthest regions of your body and reaches
every living cell. In organisms like us that
walk upright blood travels long distances
directly uphill. The blood is in constant
rapid motion; a drop of blood may make
the rounds of the body in less than half
a minute. How is it done?

Blood is moved in the simplest way;
it is pushed. If a liquid is put into a bag
and the bag squeezed, the liquid will
squirt out of the bag through any open-
ing. If all openings but one are closed
and the bag is squeezed hard, the liquid
will squirt out with force. The heart is
so constructed that this happens every
time it "beats." The walls of the heart
are made of powerful muscles which by
contracting do the squeezing themselves.
It is so easy to obtain a beef heart which
is constructed like yours that you will

want to do Exercises 4 and 5 to learn
about your heart.

The heart of a human being consists
of four parts. Two of these, the upper
ones, push the blood into the lower ones;
they do this gently. They are the right
and left auricles (ori-k'ls), thin- walled
chambers which collapse when not filled
with blood. The other two chambers lie
below the auricles. They are called ven-
tricles (ven'tri-k'ls), the right and left
ventricle. They are larger chambers with
much thicker walls. By contracting they
squirt the blood into big vessels carrying
blood away from the heart. They con-
tract with great force. The right and left
sides of the heart are completely sepa-
rated from one another by a thick and
solid wall. Blood cannot pass directly
from one side to the other. It is just
as though there were two distinct hearts.

The outer walls of the two auricles and
the two ventricles are continuous so that
from the outside the heart looks as

2 14 ^ How a Complex Anifual Uses Food unit iv

though it were one big mass of muscle.
Connected to this mass are numerous
blood vessels. They all seem to be con-
nected to the upper portion, but \^'hen
you cut the heart open and trace each
vessel to its origin vou will see that they
are connected with different chambers.
Some are connected with the auricles;
they are called veins. Veins carry blood
to the auricles. Each ventricle has one
large vessel connected to it; through
these vessels blood flows away from the
heart. Any blood vessel that carries blood
away from the heart is known as an
artery.

You can gather from what you read
above that the contraction, or beat, of
the heart occurs in two stages: the con-
traction of the two auricles, followed by
the contraction of the two ventricles.
This occurs about 70 times per minute
and never stops throughout your life. A
frog's heart, which is slightly different
from ours in structure, shows this double
beat very clearly. It will be worth while
to dissect a frog and do Exercise 6. This
demonstration shows another interesting
thing about heart muscle, whether in us
or in the frog. It can contract rhythmi-
cally by itself without being connected
to the nervous system. This is not true of
the voluntary muscle in the arm or leg
or other parts of the body; nor is it true
of the involuntary muscle in the walls
of the alimentary canal. Heart muscle not
only acts differently from the other mus-
cles but looks different from voluntary
and involuntary muscle under the micro-
scope.

William Harvey. You have probably
known for a long time about the beating
of the heart and how the blood flows

through the arteries and veins. But it
took very many centuries for us to gain
an understanding of what seems so com-
monplace now. Before men knew that
the body is made of living cells which
are supplied with digested food and oxy-
gen by the blood, they imagined all kinds
of possible uses for the blood and for the
heart. For a long time the heart was be-
lieved to be the seat of intelligence. Later
it was supposed to add "vital spirits" to
the blood. The Greeks believed that the
arteries carried air, the veins carried
blood. Theories such as these had been
largely discarded, and studies of the
structure and uses of the heart had been
begun by the beginning of the 17th cen-
tury but had never been carried very far.
William Harvey (i 578-1 667), an Eng-
lish physician, after careful studies and
after performing many accurate experi-
ments, published the book which ex-
plained the circulation of the blood as we
now understand it. He showed that the
heart is muscular and serves as a pump.
He calculated that if the heart contains
two ounces of blood and beats sixty-five
times a minute, then it drives ten pounds
of blood out into the body in less than
a minute. Evidently, the same blood is
continually being pumped around; this
amount of blood could not possibly be
made anew in that space of time. He
knew, therefore, that blood which leaves
the heart must return to the heart. If
the arteries carry it away from the heart,
the veins must bring it back. Harvey did
not see the microscopic capillaries but he
suspected that there must be tiny blood
vessels, too small for him to see, through
which blood from the arteries flows to
the veins in all parts of the body.

PROBLEM 3. Hoiv Materials Are Moved to and fro7Ji Cells

Fig. 216 What layers do
you find in the walls of ar-
teries and veins? Which have
thicker walls? Hoiv do cap-
illaries differ from arteries
and veins?

Outside connective tissue
jscular

lastic

Cell nucleus

Artery

Arteries help move the blood. The ven-
tricles contract so forcibly that the blood
is squirted well along the artery. When
a large artery is cut \'ou can see the
blood coming out in spurts. Do you know
what first aid procedure to use when an
artery is cut? Various procedures may
be used: pressure at certain points or a
tourniquet are most common. It would
be \\t\\ if all of us joined a first aid class
and learned how to stop bleeding.

The arteries which are attached to
each of the two actively pumping ven-
tricles have walls which contain a large
amount of elastic tissue. This is true of
all arteries, even those that are at some
distance from the heart. As each rush of
blood strikes these elastic walls, the ar-
tery stretches and at once comes together
again, as any elastic substance tends to do.
In this way the blood is squeezed within
the artery and helped along its course.
You can feel the walls of an artery pul-
sating (beating) whenever you put your
finger over an artery that lies near the
surface. In most parts of your body the
arteries are buried deep within the tis-
sues, but in your temples, in your wrists,
and in some other places they are close
to the skin. Here you can feel them
stretching with each squirt of blood.

Smooth
lining membrane

Capillary

■i ^

t^^r^r^t^*^':;^

Fig. 217 A piece of a cat's intestine showing
hrajiching arteries and veins. William Harvey
saw small arteries and veins, but he could not
see that they were coijnected. How are they
co7inected? (clay adams co.)

This stretching of the artery is called
the pulse. Each pulse beat is caused by
the rush of blood sent along the artery
with each contraction or pump of the
heart. Thus, counting your pulse is a
convenient way of counting your heart-
beats. Whenever your heart beats faster
you can notice this difference in your
pulse. Try Exercise 7.

A closer look at arteries. The arteries
which arise in the heart soon branch so
that the blood goes in several directions.

2l6

How a Complex Animal Uses Food unit iv

Fig. 2i8 Taking blood pres-
sure. JVhat causes blood
pressure? Why should per-
sons who have abnory/ially
high blood pressure be care-
ful not to exercise stretiu-
ously? (encyclopaedia bri-

TANNICA FILMS, INC.)

These branches subdivide again and again
so that small arteries reach all parts of
the body. In the figure of the cat's in-
testine you see a small artery subdivided
into still smaller arteries.

The walls of an artery are thick com-
pared with those of veins and especially
compared with the capillary wall. An
artery is lined inside with a thin and
very smooth membrane {serous mem-
brane) which obstructs the flow of
blood very little. Outside the inner mem-
brane is the elastic tissue. Outside the
elastic tissue lie rings of involuntary
muscle. See Figure 216. Nerve messages
that cause the muscles to contract make
the bore of the artery smaller; in other
words the artery can carry less blood.
On the other hand when these muscles
are completely relaxed the artery is a far
wider artery. In which condition is the
artery leading to your face when you
are blushing? In which condition, nor-
mally, would the artery to the small in-
testine be when digestion and absorption
are going on? Since these muscles in the
walls of arteries are involuntary, all the
changes in the size of arteries go on with-

out conscious control and often without
your knowing it.

Blood Pressure. When the heart pushes
blood into an artery it does so with great
force; the blood, in its turn, pushes
against the wall of the artery. The pres-
sure against the wall of the artery is very
great; if the wall were rigid and brittle
it might break. An elastic artery wall ex-
pands, however, thus reducing the pres-
sure on it. When we are young our
arteries are very elastic and our blood
pressure is said to be low. As a rule after
we are about forty years of age our ar-
teries slowly become less elastic and our
blood pressure grows greater. This is
normal; only unusually great increases in
blood pressure are dangerous. Physicians
measure blood pressure by using a device
that stops the flow of blood in an artery
by pressing against the artery wall. A
mercury gauge measures the pressure it
takes to press the walls of the artery to-
p-ether so that the flow of blood is
stopped; this indicates the pressure of the
blood against the artery wall.

Of course, your blood pressure rises
when your heart beats harder. For this

Fig. 219 In A a vem is bulged at the poiiit
where a valve has stopped the backward flow
of blood. In B a vem is ctit open through the
valve. In which direction does blood flow in
this vein?

PROBLEM 3. How Materials Are Moved to and fro?H Cells

reason a person whose blood pressure is
abnormally high should not engage in
strenuous exercise. The pressure may
rise so much that some smaller vessel may
burst, allowing the blood to escape into
surrounding tissues. If this happens in
the brain there is a cerebral hemorrhage.
As the blood escapes and clots, it causes
temporary or permanent paralysis by
damaging the delicate brain cells.

Fainting. It sometimes happens, for a
variety of reasons, that the heartbeat is
not forceful enough to push the blood
uphill into the arteries running into the
head. You may have seen a person's face
and lips grow pale suddenly. Blood in
sufficient amounts is not being sent up
into the head; the person loses conscious-
ness and loses control of his skeletal
muscles; he faints. Frequently he can
avoid fainting by holding his head down
between his knees or lying flat on his
back. Fainting in most cases is not a sign
of any special defect. But it should be
called to the attention of a physician if
it occurs repeatedly.

An aviator may have a similar experi-
ence. When he makes a very fast and
sharp turn or pulls out of a fast dive
sharply, the blood in his body is pushed
toward the outside of the curve. Since
this is away from the head, the blood
pressure may not be great enough to
force blood to the arteries of the head.
As soon as the brain cells fail to receive
the necessary oxygen unconsciousness
occurs. This is the "blackout" pilots talk
about. They "see black" as they faint.
As soon as the pressure of blood coming
from the heart is greater than the force
pushing the blood back the aviator re-
covers.

217

Blood returns by means of veins. The

finest branches of arteries open into
capillaries. Here the spurting motion of
the blood is lost. It flows more slowly
and smoothly, pushed by the force of the
blood behind it in the arteries. From the
network of microscopic capillaries which
lie in every part of the body, the blood
flows into wider vessels, the veins. These
unite with one another, forming larger
and larger veins, the largest of which
empty into the heart. Their walls con-
tain some elastic tissue, but since the
blood lost its spurting motion in the
capillaries it flows smoothly through the
veins, forced onward largely by the
pressure of the blood behind.

But the pressure of blood flowing in
the capillaries is not always sufficient to
push blood uphill. The blood in the veins
of the legs, for example, may tend to
stop and flow backward. This is pre-
vented by valves which are flaps like

Head

Chest and arms

Right auricle

Kidneys

Legs-

Left ventricle

Liver

Stomach
and intestines

Fig. 220 Diagram of circulatio?? of blood from
left ventricle to right auricle. Blood is forced
out of the left ventricle through the aorta.
Through what large organs does it flow?
Branches to some of the smaller organs are not
shown here. What kind of blood vessels are
shown in black? Does tl^e blood in them con-
tain iimch or little oxygen? See Figure 221 for
circidation from right ventricle to left auricle.

How a Complex Aiih/ial Uses Food unit iv

to move it onward. There is another
force that keeps the blood moving on-
ward to the heart. When you move
about, particularly when you exercise
actively, the inner parts of your body
press against one another. Muscles, and
even many of the internal organs, change
size and shape constantly. As they do this
they squeeze the veins within them or
next to them. When the vein is squeezed
the blood moves forward toward the
heart since the valves prevent it from
going backward.

Eventually it reaches the auricles and
flo\\s into them with a steady flow. But
when the auricles are full, the muscles of
their walls contract and force the blood
into the ventricles below.

The course of the blood. Imaoine that
you are small enough to seat yourself on
one of the red corpuscles for a ride
around the body. Suppose you started
from the left ventricle arid were shot into
the large artery known as the aortal (av-
or'ta). Soon the aorta branches, one
branch leading to the head, another to
the arms. At this point you might part
company with some of your friends who
were riding on other corpuscles. You
continue, let us say, down the main ar-
tery toward the legs. But immediately
you are saying good-by again to more
of your friends, some of whom turn off
to the stomach, some to the intestine, and

patch pockets on a coat. The valves oc-
cur at regular distances all along the
veins. See Figure 2 19. If now you will take
time to do Exercise 8, you will learn how
to find the location of some of the valves
in the veins of your arm or hand.

Valves can prevent the blood from
flowing backward but they have no force

some to other internal organs. The ar-
tery along which you are travelling has
become a narrower tube and iww
branches equally, one branch leading
down each leg. "S'ou happened to go into
the left branch and soon find yourself
in the left foot, in a very small artery.
Suddenh' things look different to you.

PROBLEM 3. HouD Materials Are Moved to arid from Cells

Right lung
Fig. 221 Circulation of blood

from right vetitricle to left
auricle. Blood from the right
ventricle goes only to the
lungs. The black vessels are
arteries. Does the blood in
the shaded vessels contain
much or little oxygen? Are
the shaded vessels veins or
arteries? What happens to
the blood as it passes through
the capillaries of the lungs?
To which chamber does it
go from the lungs?

219

Left lung

The tube is extremely narrow and you
can look out through its walls. You are
now in a capillary with very thin, trans-
parent walls. Here the corpuscle on
which you are riding changes color.
Oxygen leaves the hemoglobin and dif-
fuses into the neighboring cells. The
plasma in which your corpuscle is float-
ing is also undergoing changes, for foods
are diffusing out of the capillary and the
wastes of oxidation from the neighbor-
ing cells are entering the capillary. But
you never stop for any of these changes
to take place. On you go, noticing soon
that you are again in a slightly wider
tube and you cannot look out any more.
You have left the capillary. You are in a
vein and you are travelling straight up-
hill. You soon notice that you are joined
again by corpuscles that had been down
to the right foot. Then you meet the
friends who had travelled through the
stomach, the intestines, and other organs
in the abdominal cavity. You are by this
time riding in a very wide tube. This
wide tube (called the inferior vena cava)
connects with the right auricle and you
soon find yourself dropped into the right

Right
ventricle

auricle. Examine Figure 220 to trace your
course and that of some of your friends.
Figures 220 and 221 are diagrams to
make clear the course of the blood.

You are now back in the heart but not
where you started from. You are on the
right side; you started from the left. In
this right auricle occurs